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Abstract:

The present invention provides a method for producing stereo complex
crystals of polylactic acid, with which a polylactic acid having
excellent heat resistance and containing stereo complex crystals at a
high ratio can be efficiently produced, the method including: a step of
dissolving in a solvent a block copolymer, which includes polylactic acid
containing an L-lactic acid unit or poly lactic acid containing a
D-lactic acid unit together with at least one kind of an organic polymer
having a different structure from that of polylactic acid, and a
polylactic acid homopolymer containing a D-lactic acid unit or a
polylactic acid homopolymer containing an L-lactic acid unit, the lactic
acid unit being an optical isomer that is not contained in the block
copolymer, to prepare a polymer mixture solution; and a step of removing
the solvent from the polymer mixture solution.

Claims:

1. A method for producing stereo complex crystals of polylactic acid, the
method comprising: dissolving, in a solvent, to prepare a polymer mixture
solution: a block copolymer comprising at least one kind of organic
polymer having a different structure from polylactic acid and polylactic
acid containing an L-lactic acid unit or polylactic acid containing a
D-lactic acid unit; and a polylactic acid homopolymer containing a
D-lactic acid unit that is an optical isomer that is not contained in the
block copolymer or a polylactic acid homopolymer containing an L-lactic
acid unit that is an optical isomer that is not contained in the block
copolymer; and removing the solvent from the polymer mixture solution to
obtain a polymer mixture.

2. The method for producing stereo complex crystals of polylactic acid
according to claim 1, the method further comprising performing a heat
treatment after removing the solvent from the polymer mixture solution.

3. The method for producing stereo complex crystals of poly lactic acid
according to claim 1, wherein, in the polymer mixture solution, a content
ratio of the polylactic acid containing an L-lactic acid unit or the
polylactic acid containing a D-lactic acid unit, which is contained in
the block copolymer, relative to the content of the polylactic acid
homopolymer containing a D-lactic acid unit or the polylactic acid
homopolymer containing an L-lactic acid unit is in a range of from 10:90
to 90:10.

4. The method for producing stereo complex crystals of polylactic acid
according to claim 1, wherein, in the polymer mixture solution, the
molecular weight of the polylactic acid containing an L-lactic acid unit
or the polylactic acid containing a D-lactic acid unit, which is
contained in the block copolymer, is from 10,000 to 1,000,000.

5. The method for producing stereo complex crystals of polylactic acid
according to claim 1, wherein, in the polymer mixture solution, the
molecular weight of the polylactic acid homopolymer containing a D-lactic
acid unit or the polylactic acid homopolymer containing an L-lactic acid
unit is from 10,000 to 1,000,000.

6. The method for producing stereo complex crystals of polylactic acid
according to claim 2, wherein the heat treatment of the obtained polymer
mixture is performed at a heat treatment temperature in a range of from
100.degree. C. to 250.degree. C. for a heat treatment time in a range of
from 1 minute to 72 hours.

8. The method for producing stereo complex crystals of polylactic acid
according to claim 1, wherein the organic polymer having a different
structure from polylactic acid comprises one or more kinds selected from
the group consisting of polystyrenesulfonic acid, polyethylene glycol,
polyethylene oxide, poly-n-propyl-p-styrenesulfonic acid, polyacrylamide,
polydimethylacrylamide, poly-N-isopropylacrylamide,
poly-2-(N,N-dimethylamino)ethyl methacrylate,
poly-N-2-hydroxypropyl-methacrylamide, and derivatives thereof.

9. The method for producing stereo complex crystals of polylactic acid
according to claim 1, wherein, in the block copolymer comprising at least
one kind of organic polymer having a different structure from polylactic
acid and polylactic acid containing an L-lactic acid unit or polylactic
acid containing a D-lactic acid unit, the content ratio of the polylactic
acid containing an L-lactic acid unit or the polylactic acid containing a
D-lactic acid unit relative to the organic polymer having a different
structure from polylactic acid is in a range of from 10:90 to 90:10.

10. A polylactic acid obtained by the method for producing stereo complex
crystals of poly lactic acid according to claim 1, having a content ratio
of stereo complex crystals of 10% by mass or higher, with respect to the
total amount of the polylactic acid components, a content ratio of the
organic polymer having a different structure from polylactic acid of from
1% by mass to 99% by mass, and a melting point of from 220.degree. C. to
260.degree. C.

11. A molded body comprising the polylactic acid according to claim 10.

12. A synthetic fiber comprising the polylactic acid according to claim
10.

13. A porous body formed by decomposing and removing a component other
than polylactic acid from of the polylactic acid according to claim 10.

14. An ion conductor formed by applying an ion source to a component
other than polylactic acid which is contained in at least any of the
polylactic acid according to claim 10.

15. A porous body formed by decomposing and removing a component other
than polylactic acid from the molded body according to claim 11.

16. A porous body formed by decomposing and removing a component other
than polylactic acid from the synthetic fiber according to 12.

17. An ion conductor formed by applying an ion source to a component
other than polylactic acid which is contained in the molded body
according to claim 11.

18. An ion conductor formed by applying an ion source to a component
other than polylactic acid which is contained in the synthetic fiber
according to claim 12.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a method for producing stereo
complex crystals of polylactic acid, a polylactic acid obtained by the
production method, and a molded body, a synthetic fiber, a porous body,
and an ion conductor respectively containing the polylactic acid, and
more specifically, the present invention relates to a method for
producing stereo complex crystals of polylactic acid, with which a
polylactic acid having a higher content of stereo complex crystals than
those of conventional polylactic acids can be efficiently produced; a
polylactic acid which is obtained by the production method, has a high
melting temperature and is useful for forming a molded body, a synthetic
fiber, a porous body, or an ion conductor; and a molded body, a synthetic
fiber, a porous body, and an ion conductor respectively containing the
polylactic acid.

BACKGROUND ART

[0002] Recently, biomass resins obtainable from plant-based components as
raw materials have been attracting much attention, as compared with
conventional synthetic resins synthesized from petroleum, and various
studies have been made of biomass resins. Such plant-derived resins are
carbon neutral materials, since, even if they are burned during disposal,
plants absorb the generated carbon dioxide to undergo photosynthesis and
become raw materials, and replacement of conventional synthetic resins
with these plant-derived resins is expected to be a method that
contributes to the prevention of global warming. As these resins derived
from living organisms, polyhydroxybutyrate, polylactic acid, and the like
are known, and among these, polylactic acid has attracted much attention
since polylactic acid is advantageous in that lactic acid, lactides, or
the like, which are obtainable from plant resources such as corn, can be
used as a raw material, and that polylactic acid has thermal plasticity
and can be fabricated by melting. However, the melting point of general
polylactic acid is about 170° C., and therefore, improvement in
heat resistance has been required for their application to resin molded
bodies or a synthetic fibers.

[0003] Poly-L-lactic acid (hereinbelow, as appropriate, referred to as
"PLLA"), which is composed of only an L-lactic acid unit, which is an
optical isomer, and poly-D-lactic acid (hereinbelow, as appropriate,
referred to as "PDLA"), which is composed of only a D-lactic acid unit,
exist as polylactic acids, and it is known and noted that, when these
make a pair and are filled in a crystal lattice to generate a stereo
complex crystal, an increase in the melting point is realized.

[0004] For example, it is known that when PLLA and PDLA are mixed together
in the state of a solution or in a molten state, stereo complex crystals
are formed (see Japanese Patent Application Laid-Open (JP-A) No.
63-241024, Macromolecules, Vol. 24, pages 5651-5656 (1991) and Polymer,
Vol. 49, pages 5670-5675 (2008)). These stereo complex crystals have a
melting point higher than that of α crystal (melting point
170° C.) obtainable from a homopolymer of PLLA or PDLA, and
exhibit resistance to hydrolysis; however, when the molecular weight of
PLLA or PDLA, which is used as a raw material, is high, it is hard to
efficiently obtain stereo complex crystals. In addition, there are
problems in that the yield of stereo complex crystals differs according
to the conditions for preparation such as the molecular weight of the raw
material or the mixing temperature, and that it takes a lot of time to
grow, and the like, and thus, in practice, stable production of stereo
complex crystals has not yet been realized.

[0005] Further, an attempt has been made to generate stereo complex
crystals having a melting point higher than those of α crystals, by
mixing a homopolymer of PLLA and a homopolymer of PDLA at a ratio of 1:1
(see, for example, Macromolecules, Vol. 24, pages 5651-5656 (1991) and
Polymer, Vol. 49, pages 5670-5675 (2008)); however, the melting point of
the stereo complex crystal to be obtained is 230° C. at highest,
and there is still room for improvement in heat resistance in order to
enable application to molded bodies or synthetic fibers.

[0006] Moreover, a method of melt-mixing or solution-mixing copolymers
containing an L-lactic acid block and a D-lactic acid block, the
copolymers having different composition ratios from each other, to
prepare a polylactic acid having a high content of stereo complex
crystals has been proposed (see, for example, JP-A No. 2007-191625).
However, in this production method, the processes are complicated in
that, first, plural copolymers containing a L-lactic acid block and a
D-lactic acid block are prepared, and the melting point of the obtained
polylactic acid is from 147° C. to 211° C., and therefore,
the obtained polylactic acid is less likely to be applied to a material
for a molded body or the like that needs to have heat resistance.

[0007] For this reason, a technique for stably and efficiently producing a
polylactic acid that contains stereo complex crystals at a high ratio and
has excellent heat resistance is required.

DISCLOSURE OF INVENTION

Technical Problem

[0008] The object of the present invention is to provide a method for
producing stereo complex crystals of polylactic acid, with which a
polylactic acid having excellent heat resistance and containing stereo
complex crystals at a high ratio can be produced.

[0009] Another object of the present invention is to provide a polylactic
acid which is obtained by the production method of the present invention,
contains stereo complex crystals at a high ratio, and has excellent heat
resistance; and a molded body and a synthetic fiber, which are obtained
by using the polylactic acid or by containing the polylactic acid, and
have excellent heat resistance, biocompatibility, transparency, and
chemical stability.

[0010] Moreover, yet another object of the present invention is to provide
a porous body by decomposing and removing the component other than
polylactic acid from the molded body or the synthetic fiber. Further, yet
another object of the present invention is to provide an ion conductor by
applying an ion source to the component other than polylactic acid.

Solution to Problem

[0011] The present inventors conducted investigations with a view to
achieving the above objects and, as a result, it has been found that the
above objects can be attained by a method for producing a polylactic acid
containing stereo complex crystals at a high content ratio, using a block
copolymer in which PLLA or PDLA and a polymer compound other than
polylactic acid are covalently bonded together, whereby the present
invention has been completed.

[0012] Namely, the configuration of the present invention is as follows.

[0013] The invention according to claim 1 is

[0014] a method for producing stereo complex crystals of polylactic acid,
the method including: a step of dissolving in a solvent, to prepare a
polymer mixture solution: a block copolymer including at least one kind
of an organic polymer having a different structure from polylactic acid
and polylactic acid containing an L-lactic acid unit or polylactic acid
containing a D-lactic acid unit; and a polylactic acid homopolymer
containing a D-lactic acid unit that is an optical isomer that is not
contained in the block copolymer or a polylactic acid homopolymer
containing an L-lactic acid unit that is an optical isomer that is not
contained in the block copolymer; and a step of removing the solvent from
the polymer mixture solution to obtain a polymer mixture.

[0015] In this production method, after the step of removing the solvent
from the polymer mixture solution, a heat treatment step may further be
carried out, as the invention described in claim 2.

[0016] In this process, regarding the chemical structure of the block
copolymer to be used, it is enough that the block copolymer is a
copolymer composed of plural block components including polylactic acid,
for example, diblock (two kinds of components including polylactic acid),
triblock (three kinds of components including polylactic acid),
tetrablock (four kinds of components including polylactic acid),
pentablock (five kinds of components including polylactic acid), or the
like. Further, the copolymer may be a star-like block copolymer in which
plural blocks including polylactic acid radiate in all directions.

[0017] The invention according to claim 3 is

[0018] the method for producing stereo complex crystals of polylactic acid
described in claim 1 or claim 2, wherein, in the polymer mixture
solution, a content ratio of the polylactic acid containing an L-lactic
acid unit or the polylactic acid containing a D-lactic acid unit, which
is contained in the block copolymer, relative to the content of the
polylactic acid homopolymer containing a D-lactic acid unit or the
polylactic acid homopolymer containing an L-lactic acid unit is in a
range of from 10:90 to 90:10.

[0019] The invention according to claim 4 is

[0020] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 3, wherein, in the polymer
mixture solution, the molecular weight of the polylactic acid containing
an L-lactic acid unit or the polylactic acid containing a D-lactic acid
unit, which is contained in the block copolymer, is from 10,000 to
1,000,000.

[0021] The invention according to claim 5 is

[0022] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 4, wherein, in the polymer
mixture solution, the molecular weight of the polylactic acid homopolymer
containing a D-lactic acid unit or the polylactic acid homopolymer
containing an L-lactic acid unit is from 10,000 to 1,000,000.

[0023] The invention according to claim 6 is

[0024] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 5, wherein the step of heat
treating the obtained polymer mixture is a step of heat treating at a
heat treatment temperature in a range of from 100° C. to
300° C. for a heat treatment time in a range of from 1 minute to
72 hours.

[0025] The invention according to claim 7 is

[0026] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 6, wherein the organic polymer
having a different structure from that of polylactic acid is one or more
kinds selected from the group consisting of polystyrene, polyvinyl
naphthalene, polymethyl methacrylate, poly-.di-elect cons.-caprolactone
(polycaprolactam), polybutadiene, polydimethylsiloxane, polyethylene,
polypropylene, poly-1-butene, poly-4-methyl-1-pentene, polynorbornenyl
ethylstyrene, polynorbornenyl ethylstyrene-s-styrene, polyhexamethyl
carbonate, polyhexylnorbornene, polybutyl succinate,
polydicyclopentadiene, polycyclohexyl ethylene, poly-1,5-dioxepan-2-one,
polymenthide, poly-4-vinylpyridine, polyisoprene, poly-3-hydroxybutyrate,
poly-2-hydroxymethacrylate, poly-N-vinyl-2-pyrrolidone,
poly-4-acryloylmorpholine, and derivatives thereof.

[0027] The invention according to claim 8 is

[0028] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 6, wherein the organic polymer
having a different structure from that of polylactic acid is one or more
kinds selected from the group consisting of polystyrenesulfonic acid,
polyethylene glycol, polyethylene oxide, poly-n-propyl-p-styrenesulfonic
acid, polyacrylamide, polydimethylacrylamide, poly-N-isopropylacrylamide,
poly-N,N-dimethylamino-2-ethyl methacrylate,
poly-N-2-hydroxypropyl-methacrylamide, and derivatives thereof.

[0029] The invention according to claim 9 is

[0030] the method for producing stereo complex crystals of polylactic acid
described in any one of claim 1 to claim 8, wherein, in the block
copolymer including at least one kind of an organic polymer having a
different structure from that of polylactic acid and polylactic acid
containing an L-lactic acid unit or polylactic acid containing a D-lactic
acid unit, the content ratio of the polylactic acid containing an
L-lactic acid unit or the polylactic acid containing a D-lactic acid unit
relative to the organic polymer having a different structure from that of
polylactic acid is in a range of from 10:90 to 90:10.

[0031] The invention according to claim 10 is

[0032] a polylactic acid obtained by the method for producing stereo
complex crystals of polylactic acid according to any one of claim 1 to
claim 9, having a content ratio of stereo complex crystals relative to
the polylactic acid component of 10% by mass or higher, and a content
ratio of the organic polymer having a different structure from that of
polylactic acid of from 1% by mass to 99% by mass, and having a melting
point of from 220° C. to 260° C.

[0033] The invention according to claim 11 is

[0034] a molded body configured to include the polylactic acid described
in claim 10.

[0035] The invention according to claim 12 is

[0036] a synthetic fiber configured to include the polylactic acid
described in claim 10.

[0037] The invention according to claim 13 is

[0038] a porous body formed by decomposing and removing a component other
than polylactic acid from at least any of the polylactic acid described
in claim 10, the molded body described in claim 11, or the synthetic
fiber described in claim 12.

[0039] The invention according to claim 14 is

[0040] an ion conductor formed by applying an ion source to a component
other than polylactic acid, which is contained in at least any of the
polylactic acid described in claim 10, the molded body described in claim
11, or the synthetic fiber described in claim 12.

[0041] The function of the present invention is not clear, but is guessed
as follows.

[0042] In the production method of the present invention, first, a block
copolymer containing PLLA or PDLA and a polymer compound other than
polylactic acid is synthesized. To this, a PDLA homopolymer or a PLLA
homopolymer, the homopolymer being an optical isomer that is not
contained in the block copolymer, is added, and the two components are
dissolved in a solvent and mixed. For example, when a diblock copolymer
(PS-b-PLLA) containing polystyrene (PS) and PLLA as block copolymer
components is used for explanation, it is thought that, after dissolving
in a solvent the block copolymer and a PDLA homopolymer, as the solvent
is removed, the polystyrene component in the block copolymer and a
component, which is obtained by fusing the PLLA component in the block
copolymer and the PDLA homopolymer, form a phase separated structure in
nano-meter order, and in the phase separated structure, the PLLA portion
derived from the block copolymer and the PDLA in the PDLA homopolymer
added are present close to each other, and thus, stereo complex crystals
are formed efficiently. Therefore, as compared with the conventional
method in which a PLLA homopolymer and a PDLA homopolymer are mixed in a
solvent and then the solvent is removed, due to the formation of stereo
complex crystals in a close state in the phase separated structure, the
remaining of a phase derived from the homopolymer is suppressed,
resulting in achieving a higher content ratio of stereo complex crystals.
Further, since the polylactic acid component including the stereo complex
crystals is kept in a nano-sized phase separated structure formed with
polystyrene, the polylactic acid component is in a restricted state, and
therefore, it is thought that the polylactic acid component has more
excellent heat resistance than that of the stereo complex crystals
prepared from a PLLA homopolymer and a PDLA homopolymer.

[0043] It should be noted that the term "polylactic acid" described in
claim 10 of the present specification refers to the polylactic acid
obtained by the production method of the present invention, and is a
polylactic acid-containing polymer mixture that contains an additional
polymer due to the production method, together with the stereo complex
crystals. In the present specification, hereinbelow, the term "polylactic
acid of the present invention" refers to such a "polylactic
acid-containing polymer mixture".

Advantageous Effects of Invention

[0044] According to the present invention, a method for producing stereo
complex crystals of polylactic acid, with which a polylactic acid having
excellent heat resistance and containing stereo complex crystals
(hereinbelow, appropriately, referred to as "SC crystals") at a high
ratio can be efficiently produced, may be provided.

[0045] Further, according to the present invention, a polylactic acid
which has excellent heat resistance, contains stereo complex crystals at
a high ratio, and is useful for the production of a molded body, a
synthetic fiber, a porous body, an ion conductor, and the like, and a
molded body, a synthetic fiber, a porous body, and an ion conductor which
are obtained by using the polylactic acid of the present invention or by
containing the polylactic acid, and have excellent heat resistance may be
provided.

BRIEF DESCRIPTION OF DRAWINGS

[0046]FIG. 1 is a graph showing the results of DSC measurement used for
the measurement of melting points of the polylactic acids obtained in
Example 1 and Example 2.

[0047]FIG. 2 is a scanning probe microscope image showing a porous body
structure of a membrane formed from a polymer mixture which contains the
polylactic acid obtained in Example 1.

[0048]FIG. 3 is a graph showing the results of DSC measurement used for
the measurement of melting points of the polylactic acids obtained in
Example 1A.

[0049]FIG. 4 is a graph showing the results of DSC measurement used for
the measurement of melting points of the polylactic acids obtained in
Example 1B.

[0050] FIG. 5 is a graph showing the results of WAXD measurement of the
films obtained in Example 4, Comparative Example 1-1, and Comparative
Example 4; in the graph, the vertical axis shows the diffraction
intensity (in an arbitrary unit) and the horizontal axis shows the
scattering vector (q).

[0051]FIG. 6 is a graph showing the results of DSC measurement of the
films obtained in Example 4, Example 5, and Example 6.

[0052]FIG. 7 is a graph showing the results of DSC measurement of the
films obtained in Example 7.

[0053]FIG. 8 is a graph showing the results of DSC measurement of the
film obtained in Example 8

[0054]FIG. 9 is a graph showing the results of light transmittance
measurement of the film obtained in Example 8.

[0055] FIG. 10 is a graph showing the results of DSC measurement of the
film obtained in Example 9.

[0056]FIG. 11 is a graph showing the results of DSC measurement of the
films obtained in Example 10.

[0057]FIG. 12 is a graph showing the results of DSC measurement of the
films obtained in Example 11

[0058] FIG. 13 is a graph showing the results of DSC measurement of the
films obtained in Comparative Example 1.

[0059] FIG. 14 is a schematic diagram illustrating a preparation procedure
of the molded films used in Example 12 and Example 13.

[0060]FIG. 15A is a scanning probe microscope observation image of the
film obtained in Example 13.

[0061]FIG. 15B is an enlarged fragmentary view of the region surrounded
by dotted lines shown in FIG. 15A of a film obtained in Example 13.

[0064] The method for producing stereo complex crystals of polylactic acid
according to claim 1 of the present invention is characterized in that
the method includes: a step of dissolving in a solvent a block copolymer
including polylactic acid containing an L-lactic acid unit or polylactic
acid containing a D-lactic acid unit together with at least one kind of
an organic polymer having a different structure from that of polylactic
acid, and a polylactic acid homopolymer containing a D-lactic acid unit
or a polylactic acid homopolymer containing an L-lactic acid unit, the
lactic acid unit being an optical isomer that is not contained in the
block copolymer, to prepare a polymer mixture solution (hereinbelow,
referred to as a mixture solution preparing step); and a step of removing
the solvent from the polymer mixture solution (hereinbelow, referred to
as a solvent removing step).

[0065] The method may have a step of heat treating the obtained molded
body (hereinbelow, referred to as a heat treatment step), as necessary,
after the solvent removing step.

[0066] The above mixture solution preparing step includes two embodiments,
namely, a step of dissolving in a solvent a block copolymer including
polylactic acid containing an L-lactic acid unit and at least one kind of
an organic polymer having a different structure from that of polylactic
acid, and a polylactic acid homopolymer containing a D-lactic acid unit,
to prepare a polymer mixture solution (mixture solution preparing step
(1)), and a step of dissolving in a solvent a block copolymer including
polylactic acid containing a D-lactic acid unit and at least one kind of
an organic polymer having a different structure from that of polylactic
acid, and a polylactic acid homopolymer containing a L-lactic acid unit,
to prepare a polymer mixture solution (mixture solution preparing step
(2)), and in either case, the same effect is realized.

[0067] In the second embodiment of the present invention, a step
substantially similar to the step in the first embodiment is included
except that a block copolymer containing PDLA is used as the block
copolymer and, to this, a PLLA homopolymer is added.

[0068] Further, the solvent removing step may be carried out by any means
capable of removing the solvent from the polymer mixture liquid, and may
be, for example, any of a step of removing the solvent by vaporization
(including a solvent removing step by spin coating or by the
electrostatic spinning method), a step of removing the solvent by
filtration, a step of removing the solvent by absorbing the solvent using
filter paper or the like, or a step of adding the mixture solution to a
poor solvent that does not dissolve polylactic acid to separate the
polylactic acid; and further, these steps may be carried out alone or may
be carried out by appropriately combining them, and in a case in which
the solvent removing step includes two or more of the steps described
above, it is possible to repeat the respective steps to be carried out,
and the order and frequency may be arbitrarily selected.

[0069] After the solvent removing step, in a case in which the polymer
mixture obtained by removing the solvent forms a molded body in the form
of a membrane, a film, a sheet, powder, or the like, a further heating
step or molded body forming step may not be conducted. As described
above, the membranous or powdery solid component which is obtained after
the solvent removing step is also included in the molded body of the
present invention. After the solvent removing step, also in the case in
which a membranous or powdery molded body is formed, a heating step may
be carried out as required.

[0070] Further, a molded body having a different form from that of the raw
material molded body, such as structure or fiber, may be formed by using
the obtained molded body in the form of a membrane, powder, or the like
as a raw material and adding a further molding step. In this process, as
the molding step, a known method such as press molding, roll molding,
stretch molding (uniaxial or biaxial), kneading or extrusion molding,
injection molding, melt spinning, or electrostatic spinning may be
utilized.

[0071] As described above, by using the polymer mixture body according to
the present invention, a molded body, a synthetic fiber, a porous body,
and an ion conductor, each containing the polylactic acid having
excellent heat resistance, and the like are obtained.

[0072] In this process, the above mixture solution preparing step, solvent
removing step, heat treatment step, molding step, perforating step, ion
source applying step, or the like may be repeated, and the order and
frequency may be arbitrarily selected. For example, in a case in which
the stereo complex crystallized polylactic acid obtained through the
above mixture solution preparing step and solvent removing step is again
dissolved or swelled in the solvent and is subjected to a mixture
solution preparing step, there is a case in which, even though the
dissolution conditions are the same as the conditions of the first
mixture solution preparing step, the once-formed stereo complex crystal
does not dissolve thoroughly and remains, and this acts as a nucleus in
the solvent removing step, the heat treatment step, or the molding step,
resulting in the formation of stereo complex crystals at a higher ratio.

[0073] Hereinbelow, as an example, the case of using a block copolymer
including a PLLA polymer and an additional polymer compound (an organic
polymer having a different structure from that of polylactic acid) and a
PDLA homopolymer, the case being the first embodiment of the present
invention, is explained.

[0074] <Mixture Solution Preparing Step (1)>

[0075] In this step, first, a copolymer including PLLA and a polymer
compound other than polylactic acid is prepared.

[0076] The PLLA polymer which is used for forming the block copolymer is a
polymer containing an L-lactic acid unit as a main component, should
contain the L-lactic acid unit in a proportion of 5% by weight or higher,
and is preferably a polymer consists of 100% L-lactic acid unit excluding
unavoidable impurities.

[0077] The weight average molecular weight of the PLLA polymer is
preferably from 10,000 to 1,000,000, and more preferably from 10,000 to
500,000. Further, the molecular weight distribution is preferably from 1
to 10, more preferably from 1 to 2, and even more preferably from 1 to
1.5.

[0078] Here, with regard to the molecular weight of the PLLA homopolymer,
when a compound having a high molecular weight, for example, a compound
having a molecular weight of 10,000 or more, and more preferably 50,000
or more, is used, physical properties of the obtained polylactic acid of
the present invention or the molded body formed from the polylactic acid,
especially membrane-forming property or the strength of the formed
membrane, may be improved.

[0079] The terminal of the PLLA polymer may be capped by a terminal
capping group. Examples of such a terminal capping group include an
acetylene group, an ester group, an ether group, an amido group, and a
urethane group.

[0080] The PLLA polymer may be produced by a known polymerization method
of polylactic acid, as exemplified by a method of performing ring-opening
polymerization of lactide, dehydration condensation of lactic acid, or a
combination of any one of them and solid-phase polymerization, and then
allowing melt solidification. More specifically, the PLLA polymer may be
synthesized by a living step polymerization method of lactide, which is a
cyclic dimer of lactic acid, as described in Makromol. Chem. Vol. 191,
pages 481-488 (1990) and JP-A No. 1-225622; a direct ring-opening
polymerization method of a racemic body of lactide using a specific
stereoselective polymerization catalyst, as described in JP-A No.
2003-64174; a melt polymerization method from lactic acid; or a
ring-opening method of lactide.

[0081] Further, the PLLA polymer may contain a catalyst for
polymerization, as long as the thermal stability is not damaged. Examples
of the catalyst may include aluminum compounds, lithium compounds, tin
compounds, titanium compounds, calcium compounds, organic acids, and
inorganic acids, and further, a stabilizer for deactivating the catalyst
may be coexistent.

[0083] There is no particular limitation as to the organic polymer
(hereinbelow, appropriately, referred to as the additional polymer
compound) which forms the block copolymer and has a different structure
from that of polylactic acid, but in the present invention, since it is
assumed that the block copolymer forms a micro-phase separated structure,
and in the mocro-phase separated structure, PLLA and PDLA are present
close to each other and are kept in the structure at the same time, and
thus a polylactic acid exhibiting a high melting point is obtained, it is
important that the polylactic acid (PLLA or PDLA) component and the
additional polymer compound form a micro-phase separated structure in the
block copolymer. Here, in the case of a diblock copolymer including A
polymer and B polymer, assuming that the size of A monomer and the size
of B monomer are equal, it is known that micro-phase separation occurs
when the interaction parameter (χ) of A polymer and B polymer
satisfies the following equation.

χn>10.5

[0084] In the above equation, n represents the polymerization degree of
the block copolymer. Accordingly, it is required that the additional
polymer compound in the present invention accepts this condition with
respect to the polylactic acid. This concept is described in detail in
KISO KAGAKU KOSU (Fundamental Chemistry Course), KOBUNSHI KAGAKU
II--BUSSEI-- (Polymer Chemistry II--Physical Properties--), (Maruzen Co.,
Ltd, written by Hirohide Matsushita, published in 1996) page 68, which is
herein incorporated by reference.

[0085] Further, from the viewpoint of carrying out solution mixing with
the polylactic acid homopolymer, the additional polymer compound is
preferably a polymer that can be dissolved in a common solvent with
polylactic acid. Moreover, from the viewpoint of carrying out a heat
treatment step with respect to the polylactic acid, it is preferable that
the thermal decomposition temperature is 200° C. or higher.

[0087] Among them, from the viewpoints of ease of synthesis of the block
copolymer with the coexisting PLLA polymer or PDLA polymer, having a
great interaction parameter (χ) to polylactic acid, and ease of
forming a phase separated structure, polystyrene, polyvinyl naphthalene,
polymethyl methacrylate, poly-.di-elect cons.-caprolactone,
polycaprolactam, polybutadiene, polydimethylsiloxane, polyethylene,
polypropylene, poly-1-butene, poly-4-methyl-1-pentene, polynorbornenyl
ethylstyrene, polynorbornenyl ethylstyrene-s-styrene, polyhexamethyl
carbonate, polyhexylnorbornene, polybutyl succinate,
polydicyclopentadiene, polycyclohexyl ethylene, poly-1,5-dioxepan-2-one,
polymenthide, poly-4-vinylpyridine, polyisoprene, poly-3-hydroxybutyrate,
poly-2-hydroxyethyl methacrylate, poly-N-vinyl-2-pyrrolidone,
poly-4-acryloylmorpholine, and derivatives thereof, each of which is an
organic polymer having relatively high hydrophobicity; or
polystyrenesulfonic acid, polyethylene glycol, polyethylene oxide,
poly-n-propyl-p-styrenesulfonic acid, polyacrylamide,
polydimethylacrylamide, poly-N-isopropylacrylamide,
poly-2-(N,N-dimethylamino)ethyl methacrylate,
poly-N-2-hydroxypropyl-methacrylamide, and derivatives thereof, each of
which is an organic polymer having a relatively high hydrophilicity, are
preferable.

[0088] The above additional polymer compound is suitably used in the
production method of the present invention, as the polymer compound
satisfies the above physical properties, but since the additional polymer
compound remains in the polylactic acid obtained by the production method
of the present invention and in the molded body formed from the
polylactic acid, depending on the application purpose of the polylactic
acid or the molded body, a polymer compound which is suitable to the
application purpose may be selected as appropriate from these additional
polymer compounds.

[0089] For example, in a case in which the polylactic acid obtained by the
production method of the present invention has biocompatibility and is
used in drug delivery, artificial skins, artificial blood vessels,
sutures in operation, blood purifying filters/artificial kidneys (in the
case of a porous body), or the like, a polymer compound having
biocompatibility is selected, and from such a point of view, more
specifically, polyethylene glycol, polyethylene oxide, polypropylene
glycol, polypropylene oxide, poly-.di-elect cons.-caprolactone
(caprolactam), polybutyl succinate, polydimethylacrylamide,
poly-N,N-dimethylamino-2-ethyl methacrylate, poly-3-hydroxybutyrate,
poly-2-hydroxymethacrylate, poly-N-2-hydroxypropyl-methacrylamide, and
the like are cited.

[0091] Moreover, as a substance which has a low dielectric constant and is
suitably used in electronic circuit base materials or the like,
polydimethylsiloxane and the like are cited.

[0092] In addition, as a substance that is suitable for fabricating a
rubbery elastic body, polybutadiene, polyisoprene, polyisobutylene, and
the like are cited.

[0093] From the viewpoint of having a high adhesive property to other
materials, polyethyl acrylate, polymethyl acrylate, polyisopropyl
acrylate, polybutyl acrylate, polyisobutyl acrylate, polyhexyl acrylate,
polydecyl acrylate, polylauryl acrylate, other acrylate resins, and the
like are cited.

[0094] Especially, in the case of forming a molded body, a film, a sheet,
or the like, as a substance which is likely to cause crosslinking and has
excellent mechanical strength or excellent elongation, polybutadiene,
polydimethylsiloxane, polynorbornenyl ethylstyrene, polynorbornenyl
ethylstyrene-s-styrene, polynorbornene, polyhexamethyl carbonate,
polyhexylnorbornene, polyisoprene, or the like can be selected.

[0095] Further, in the case of using the molded body of the present
invention for an ion conductor, which is described below in detail, or
the like, from the viewpoint of ease of molecular modification or having
already an ion source, polystyrene, polystyrenesulfonic acid,
polybutylstyrene, polymethylstyrene, polyvinyltoluene,
polychlorovinyl-styrene, poly-4-butylstyrene, other polystyrenes,
polyvinyl naphthalene, polysulfone, polyphenylene ether sulfide,
poly-n-propyl-p-styrenesulfonic acid, polydicyclopentadiene,
poly-3-alkylthiophene, or the like may be selected.

[0096] Further, poly-1,5-dioxepan-2-one, polymenthide, or the like can
also be used.

[0097] Moreover, from the viewpoint of ease of obtaining a polymer
compound having uniform physical properties, polystyrene, polymethyl
methacrylate, polydimethylsiloxane, poly-4-vinylpyridine,
polydimethylacrylamide, and the like are preferably described, each of
which forms a block copolymer with PLLA or PDLA, the block copolymer
being commercially available from Polymer Source, Inc. or the like.

[0098] It is enough that the polymer compound, which forms a block
copolymer with polylactic acid and has a different structure from that of
polylactic acid, contains at least one kind of the above polymer
compounds, and may be a copolymer including a polymer compound other than
the above polymer compound and the above polymer compound. Alternatively,
the additional polymer compound may be a copolymer containing two or more
of the above polymer compounds. In this case, the form of the copolymer
may be either a block copolymer or a random copolymer.

[0099] The polymer component, which forms a block copolymer with
polylactic acid and has a different structure from that of polylactic
acid, may be modified by a chemical treatment or the like, prior to the
production of stereo complex crystals or a molded body containing the
same. For example, a block copolymer including polylactic acid and
polystyrene is synthesized, then this block copolymer is sulfonated to
produce a block copolymer including polylactic acid and
polystyrenesulfonic acid, and then the resulting block copolymer may be
used as a raw material for producing the above stereo complex crystals or
the molded body containing the same. By this operation, there is attained
an advantage that a chemical treatment for applying an ion source or
biocompatibility, or for perforating may not be carried out after the
solvent removing step or the heat treatment step, or may be carried out
more efficiently.

[0100] In the block copolymer including PLLA or PDLA and the polymer
compound other than polylactic acid, the chemical structure of the
junction point between the PLLA or PDLA and the polymer compound other
than polylactic acid, or the junction point between the polymer compounds
which are other than polylactic acid and have a different structure from
each other is not particularly limited, and examples include --O--,
--COO--, --NH--, --CO--, --CH2--, --OCHCH3CH2--,
--OCHCHCH3CH2CH2--, --OCH2CH2--O--CH2--,
--CO--CH2--, --CH2CH2NH--, --SiCH3CH3--,
--SiCH3CH3--, --SiCH3CH3CH2--,
--CH2CH2O--, --COCCH3═CH--, --CH2CH2S--,
--CH2CH═CH--, and -ph-CH═CH--; and among them, --O--,
--COO--, --NH--, --CO--, --CH2--, --CH2CH2O--,
--COCCH3═CH--, and --CH2CH═CH-- are preferable.

[0101] In the block copolymer including PLLA or PDLA and the polymer
compound other than polylactic acid, when the chemical structure of the
junction point between the PLLA or PDLA and the polymer compound other
than polylactic acid, or the junction point between the polymer compounds
which are other than polylactic acid and have a different structure from
each other has such a junction point structure, the block copolymer does
not decompose at all, resulting in becoming possible to be incorporated
in the polylactic acid of the present invention or in a molded body
thereof.

[0103] When the additional polymer compound has such a terminal structure,
it becomes possible to carry out various chemical modifications of the
polylactic acid obtained by the production method of the present
invention.

[0104] The weight average molecular weight of the additional polymer
compound that forms the block copolymer is preferably from 10,000 to
1,000,000, and more preferably from 10,000 to 500,000. Further, the
molecular weight distribution is preferably from 1 to 10, more preferably
from 1 to 2, and even more preferably from 1 to 1.5.

[0105] In the block copolymer including the PLLA polymer and the
additional polymer compound, the content ratio of the PLLA polymer and
the additional polymer compound is selected as appropriate from the range
of from 1:99 to 99:1, by weight ratio, and it is preferable that the
content ratio is in a range of from 10:90 to 90:10 from the viewpoint of
allowing the stereo complex crystals to be incorporated in the member at
a greater amount.

[0106] The synthesis of the block copolymer may be conducted by a
generally used method. Specifically, for example, the block copolymer can
be produced by melt mixing or solution mixing these polymers at a
predetermined ratio according to the intended block copolymer, followed
by solidification, and further performing solid-phase polymerization.
Alternatively, the block copolymer can be produced by synthesizing the
PLLA polymer in advance, and successively allowing the polymer compound
other than polylactic acid to undergo polymerization growth at the
molecular terminal thereof. On the contrary, the block copolymer can be
produced by synthesizing the polymer compound other than polylactic acid
in advance, and successively allowing the L-lactic acid unit to undergo
polymerization growth at the molecular terminal thereof.

[0107] Regarding the synthesis method of the block copolymer using the
PLLA polymer and the additional polymer compound, reference can be made
to the methods described in, for example, J. AM. CHEM. SOC. 2002, 124,
pages 12761-12773.

[0108] One of the synthesis methods is a method using living anion
polymerization. Namely, it is a method of successively adding styrene,
and thereafter, carrying out living anion polymerization while adding a
lactide monomer. Further, a method using polystyrene whose terminal is
modified with a hydroxyl group can also be adopted.

[0109] Representative polymerization scheme is as follows.

##STR00001##

[0110] The solid-phase polymerization can be carried out at a temperature
equal to or higher than the glass transition temperature (Tg) but the
melting point (Tm) or lower, more preferably Tg or higher but a
temperature 10° C. lower than Tm or lower, and particularly
preferably Tg or higher but a temperature 50° C. lower than Tm or
lower. Tg and Tm can be measured using a differential scanning
calorimeter (DSC).

[0111] The solid-phase polymerization is preferably carried out under
reduced pressure, for example, under reduced pressure of from 0.01 hPa to
20 hPa, and preferably from 0.1 hPa to 2 hPa.

[0112] Since the polymer compounds containing an L-lactic acid unit or a
D-lactic acid unit are chemically bonded together by ester reaction or
dehydration condensation reaction, H2O is by-produced along with the
proceeding of the reaction. When they are polymerized under reduced
pressure, this by-produced water can be removed to the outside of the
reaction system, and reaction equilibrium can be shifted to a
polymerization side, which is preferable. When the pressure condition
exceeds 20 hPa, the dehydration may become insufficient, and when the
pressure condition is lower than 0.01 hPa, a further dehydration effect
is not obtained.

[0113] The solid-phase polymerization may also be carried out in an inert
gas atmosphere such as nitrogen. The solid-phase polymerization time is
at least 5 hours, and preferably from 5 hours to 50 hours. The
solid-phase polymerization temperature is preferably raised as the degree
of polymerization increases.

[0114] The reaction apparatus for carrying out solid-phase polymerization
is not particularly limited, but, for example, a concentration drier or
the like may be used, according to a batch type or continuous type
process. Further, a conical drier, drum type heater, or a belt conveyance
type or fluid bed type solid-phase polymerization apparatus or the like
may also be used.

[0115] Preferably, after the solid-phase polymerization, the terminal
group is subjected to a capping treatment to improve the thermal
stability of the formed polymer compound, and further, the catalyst and
an unreacted monomer are removed by re-precipitation or the like.

[0116] In the case of using polystyrene as the additional polymer, a
commercially available product of a diblock copolymer including PLLA and
polystyrene may be used as the block copolymer. For example, as to the
block copolymer (PLLA-b-PS) including PLLA and polystyrene, trade name:
P2642-SLA (PLLA molecular weight 19,500, PS molecular weight 21,000,
total 40,500), trade name: P2643-SLA (PLLA molecular weight 14,000, PS
molecular weight 21,000, total 35,000), and trade name: P6511-SLA (PLLA
molecular weight 17,000, PS molecular weight 21,000, total 38,000), all
manufactured by Polymer Source, Inc., are commercially available
products.

[0117] The weight average molecular weight of the block copolymer is
roughly equal to the sum of the molecular weight of the PLLA polymer and
the molecular weight of the additional polymer compound, and accordingly,
the weight average molecular weight of the block copolymer used in the
present invention is preferably from 20,000 to 2,000,000, and more
preferably from 20,000 to 1,000,000. Further, the molecular weight
distribution is preferably from 1 to 10, more preferably from 1 to 2, and
even more preferably from 1 to 1.5.

[0118] In the present invention, with regard to the weight average
molecular weight and the molecular weight distribution of the polymer,
the values determined by exclusion chromatography using tetrahydrofuran
(THF) as a solvent are adopted.

[0119] Next, the PDLA homopolymer is prepared. Preparation of the PDLA
homopolymer can be conducted in a manner substantially similar to that in
the preparation of the PLLA polymer which is used as the raw material of
the diblock copolymer, except that a D-lactic acid unit is used as the
starting material.

[0120] The weight average molecular weight of the PDLA homopolymer used
for the preparation of the polymer mixture solution is preferably from
10,000 to 1,000,000, and more preferably from 10,000 to 500,000. Further,
the molecular weight distribution is preferably from 1 to 10, more
preferably from 1 to 2, and even more preferably from 1 to 1.5.

[0122] Next, the obtained block copolymer including the PLLA polymer and
the additional polymer compound and the obtained PDLA homopolymer are
dissolved in a solvent to prepare a polymer mixture solution.

[0123] The mixture ratio of the block copolymer and the PDLA homopolymer
used for the preparation of the polymer mixture solution is selected as
appropriate from the range of from 1:99 to 99:1, but from the viewpoint
of the production efficiency of stereo complex crystals, it is preferable
to adjust the mixture ratio such that the content ratio of PLLA polymer
contained in the block copolymer and the PDLA homopolymer is within the
range of from 10:90 to 90:10.

[0124] The solvent used for the preparation of the mixture solution is not
particularly limited as long as the solvent can dissolve the above two
kinds of polymers, and preferable examples of the solvent include
chloroform, tetrahydrofuran, xylene, toluene, benzene, ethylbenzene,
dichloroethane, carbon tetrachloride, trichloroethane, dichloromethane,
chlorobenzene, methyl ethyl ketone, dichlorobenzene, and
trichlorobenzene. One kind of these solvents may be used alone, or two or
more kinds of them may be mixed and used as a mixed solvent depending on
the purpose. Further, in the case of using a mixed solvent, in addition
to the above organic solvents, for example, a solvent having a low
boiling point such as methanol or ethanol may be mixed.

[0125] The concentration of the polymer compounds in the polymer mixture
solution is preferably in a range of from 0.1% by mass to 50% by mass,
and more preferably in a range of from 0.1% by mass to 20% by mass.

[0126] In the preparation of the polymer mixture solution, the block
copolymer and the PDLA homopolymer may be separately dissolved in a
solvent and then mixed together, or one of them may be mixed with a
solvent and the other may be added to and dissolved in the resulting
liquid. Preparation of the solution may be carried out at room
temperature (25° C.), but may be carried out by heating at a
temperature of from 25° C. to the boiling point of the solvent, as
required. The mixing time is preferably in a range of from 1 minute to 24
hours, from the viewpoint of uniformly mixing the two kinds of polymers.

[0127] <Mixture Solution Preparing Step (2)>

[0128] In the second embodiment of the method for producing stereo complex
crystals of polylactic acid of the present invention, the mixture
solution preparing step (2) can be conducted in a manner substantially
similar to that in the mixture solution preparing step (1) described
above, except that a block copolymer including PDLA and a polymer
compound other than polylactic acid is used in place of the block
copolymer including PLLA and a polymer compound other than polylactic
acid, which is used in the mixture solution preparing step (1), and a
PLLA homopolymer is used in place of the PDLA homopolymer; and preferable
exemplary embodiments (examples and conditions) are also the same.

[0129] Also in this step, in the case of using polystyrene as the
additional polymer, a commercially available product of a block copolymer
(PLLA-b-PS) including PDLA and polystyrene, may be used as the block
copolymer. For example, as the block copolymer including PDLA and
polystyrene, trade name: P8980C-SLA (PDLA molecular weight 17,000, PS
molecular weight 21,000, total 38,000), manufactured by Polymer Source,
Inc., and the like are commercially available.

[0131] In the mixture solution preparing step, a polymer compound
containing polylactic acid, an additive such as an inorganic filler or a
crystal nucleating agent (for example, a substance that accelerates
stereo complex crystallization of polylactid acid, or the like), a
solvent, a metal compound, an ion, or the like may be further added, as
long as the stereo complex formation according to the present invention
is not damaged, for the purpose of applying various structures or
functions (a porous structure or ionic conductivity) to the molded body
described below.

[0132] After carrying out the mixture solution preparing step (1) or
mixture solution preparing step (2), a step of removing the solvent from
the obtained polymer mixture solution is conducted.

[0133] Any means can be used for the solvent removing step, but
representatively, the following steps (1) to (4) can be cited. In the
solvent removing step, the following steps (1) to (4) may be carried out
alone or may be carried out by appropriately combining them, and in the
case of combining plural steps, the practical order is also arbitrarily
selected.

[0134] <Step (1) of Removing the Solvent of the Polymer Mixture
Solution>

[0135] Removal of the solvent may be conducted by, for example, coating
the mixture solution on a metal plate whose surface has been treated with
polytetrafluoroethylene, and leaving this as it is at room temperature to
vaporize the solvent. Alternatively, removal of the solvent may be
conducted by casting the mixture solution on a petri dish made of Teflon
(registered trademark), and leaving this as it is at room temperature to
vaporize the solvent. Further, a mixed solvent may be placed in a
container such as the above petri dish or the like, followed by
vaporizing the solvent while stirring this using a stirring bar
(stirrer), a dynamic stirrer, a stirring rod, or the like. The
vaporization of the solvent may be conducted under atmospheric pressure,
but from the viewpoint of efficiency, the vaporization of solvent may be
conducted under reduced pressure. Regarding the conditions of pressure
reduction, since a special device for reducing pressure, such as rotary
pump, is not needed and it is possible to realize also by using a vacuum
pump, an aspirator, or a diaphragm pump, the pressure is preferably
1×10-3 Torr (1.33×10-1 Pa) or higher, and more
preferably 1×10-2 Torr (1.33 Pa) or higher.

[0136] Moreover, it is also possible to obtain a thin film, by spin
coating the mixture solution on a metal substrate or the like and let the
solvent vaporize in this state, to obtain a thin membrane. In this case,
by appropriately setting the number of revolution in the spin coating, a
desired membrane thickness can be obtained. For example, when using
ACT-300A (trade name) manufactured by ACTIVE Co., Ltd., and performing
spin coating at a number of revolution of from 100 rpm to 5,000 rpm, it
is possible to form a thin membrane.

[0137] In all cases, vaporization or drying of the solvent can be
conducted at a temperature in a range of from 0° C. to 200°
C., and preferably from 20° C. to 100° C. The drying time
is preferably from 1 minute to 72 hours, and more preferably from 1
minute to 24 hours.

[0138] Alternatively, it is possible to obtain a thin membrane by making
ultra fine fibers from the mixture solution in accordance with an
electrostatic spinning method, and vaporizing the solvent while
maintaining this state. This method is a method of directly applying a
high voltage to a polymer solution or a polymer melt, to form nano fibers
by electrical spinning, and specifically, the method described in
Biomacromolecules, 2006, Vol. 7, pages 3316-3320 can be applied.

[0139] In this method, the polymer mixture solution is placed in a
syringe, and the solution is discharged at 0.1 mL/min. In this process,
the applied voltage is -25 kV, and the surface of the drum-shaped
collection portion (having a diameter of 10 cm) is made to always revolve
at 20 cm/min. As a result, fine fiber having a diameter of from 400 nm to
970 nm and an aggregate thereof are obtained.

[0140] The fine fibers thus obtained are used for various applications,
for example, not only for non-woven fabric, but also for a base material
for cell proliferation, a filter, or the like.

[0141] The vaporization or drying of the solvent can be conducted at a
temperature in a range of from 0° C. to 200° C., and
preferably from 20° C. to 100° C. The drying time is
preferably from 1 minute to 72 hours, and more preferably from 1 minute
to 24 hours.

[0142] <Step (2) of Removing the Solvent from the Polymer Mixture
Solution>

[0143] In the second embodiment of the solvent removing step in the method
for producing stereo complex crystals of polylactic acid of the present
invention, for example, removal of the solvent may be conducted by
filtering the mixture solution. In the removal of the solvent by
filtration, a filter having a pore diameter of 10 μm or less, for
example, a membrane filter made of Teflon (registered trademark), a
porous anodic aluminium oxide membrane, or the like is used from the
viewpoint of efficiently collecting the stereo complex crystals. In this
process, for the purpose of raising the filtration speed, filtration may
be conducted under reduced pressure using an aspirator, a rotary pump, or
the like. Regarding the conditions of pressure reduction, the pressure is
preferably 1×10-3 Torr (1.33×10-1 Pa) or higher,
and more preferably 1×10-2 Torr (1.33 Pa) or higher.

[0144] The removal of the solvent by filtration can be conducted at a
temperature in a range of from 0° C. to 200° C., and
preferably from 20° C. to 100° C. The filtration time is
preferably from 1 minute to 72 hours, and more preferably from 1 minute
to 24 hours.

[0145] <Step (3) of Removing the Solvent from the Polymer Mixture
Solution>

[0146] In the third embodiment of the solvent removing step in the method
for producing stereo complex crystals of polylactic acid of the present
invention, for example, removal of the solvent may be conducted by
absorbing only the solvent of the mixture solution using filter paper or
the like. In the removal of the solvent by absorption of the solvent, a
generally used paper filter may be used, from the viewpoint of absorbing
larger amount of solvent to remove rapidly the solvent.

[0147] The absorption removal of the solvent using filter paper can be
conducted under an environment of a temperature condition of from
0° C. to 200° C., and preferably from 20° C. to
100° C. The absorption time is preferably in a range of from 1
minute to 72 hours, and more preferably from 1 minute to 24 hours.

[0148] <Step (4) of Removing the Solvent from the Polymer Mixture
Solution>

[0149] In the fourth embodiment of the solvent removing step in the method
for producing stereo complex crystals of polylactic acid of the present
invention, the mixture solution is mixed with a poor solvent that does
not dissolve polylactic acid, such as methanol, to separate the
polylactic acid, and thereafter, any one of the above solvent removing
steps (1) to (3) or a combination of these steps may be carried out to
remove the solvent.

[0150] There is a case in which a porous body is obtained by carrying out
the above solvent removing step, according to the combination of the
additional organic polymer and the solvent. This is caused because, due
to the fact that the additional organic polymer in the bock copolymer is
likely to hold the solvent, the component other than polylactic acid
involves the solvent and is in the swelled state in the former period of
the solvent removal process, even if the polylactic acid component forms
stereo complex crystals and solidifies, and therefore, the solvent is
selectively removed from the component other than polylactic acid in the
latter period of the solvent removal process, and thus this region
becomes a hole. Alternatively, depending on the solvent used, the
amorphous region (the region of polylactic acid other than the stereo
complex crystals) of the polylactic acid component involves the solvent,
and when the solvent vaporizes, a porous structure is formed. In such a
case, the polymer mixture becomes a porous body, and can be suitably
utilized as a porous body which is configured to include the polylactic
acid of the present invention, which is described below in detail.
Further, the porous body formed from the polymer mixture may further be
heat treated by performing a heat treatment step which is subsequently
performed as desired, to provide a porous body containing stereo complex
crystals at a higher ratio.

[0151] In the above solvent removing step, a polymer compound containing
polylactic acid, an additive such as an inorganic filler or a crystal
nucleating agent (for example, a substance that accelerates stereo
complex crystallization of polylactid acid, or the like), a solvent, a
metal compound, an ion, or the like may be further added, for the purpose
of applying various structures or functions (a porous structure or ionic
conductivity) to the molded body described below, as long as the stereo
complex formation according to the present invention is not damaged.

[0152] It should be noted that, in the step of fabricating a molded body,
which is described below, in the case of molding the polymer mixture in
the state of being swelled by the solvent, it is not necessary to
thoroughly remove the solvent in the solvent removing step, and the
polymer mixture involving the solvent may be used for fabricating a
molded body or a synthetic fiber by, for example, kneading, extrusion,
injection molding, press molding, melt spinning, wet spinning,
electrostatic spinning, or the like.

[0154] After carrying out the step of removing the solvent from the
mixture solution, the obtained polymer mixture generally becomes a
membrane or powder formed from the polymer mixture, and this is a
membrane or powder including stereo complex crystals of polylactic acid
at a high ratio. After the solvent removal step, it is preferable to
carry out a heat treatment step of heat treating the polymer mixture,
from the viewpoint of raising the content ratio of stereo complex
crystals.

[0155] The polymer mixture may be subjected to heat treatment in a DSC
oven, by placing the polymer mixture in a sample pan for differential
scanning calorimeter (DSC) measurement. Further, an oven, a press molding
apparatus, an air thermostat, or an oil bath, which can be set to a
constant temperature, or the like may also be used.

[0156] The polylactic acid of the present invention may be a substance
prepared by performing heat treatment on the membranous or powdery molded
body obtained through the solvent removing step, or in the case of
producing a molded body having different form, a synthetic fiber, a
porous body, or an ion conductor by using, as the raw material, the
polymer mixture or the molded body obtained by removing the solvent from
the polymer mixture, a form of a molded body, a synthetic fiber, a porous
body, or an ion conductor may be formed in advance by using the polymer
mixture or the like, and then a heat treatment may be carried out, as
described below.

[0157] The heat treatment step can be carried out at a temperature within
a range of from 100° C. to 300° C., the range being equal
to or higher than the glass transition temperature (Tg) of the polylactic
acid but the melting point (Tm) or lower, and more preferably from
150° C. to 250° C. The heat treatment time is preferably
from 1 minute to 72 hours, and more preferably from 1 hour to 24 hours.

[0158] <Polylactic Acid>

[0159] After removing the solvent, the polymer mixture obtained is a
polylactic acid, which contains stereo complex crystals at a high ratio
and has a form of a membrane or powder, and contains an additional
polymer compound derived from the block copolymer used as a raw material.

[0160] The existence of the stereo complex crystals in the polylactic acid
can be confirmed by wide-angle X-ray diffraction measurement (WAXD) or
DSC measurement. The content ratio of the stereo complex crystals in the
polylactic acid obtained by the production method of the present
invention is 10% by mass or higher with respect to the total amount of
the polylactic acid, and more preferably from 10% by mass to 100% by
mass. Further, the content ratio of α crystal is preferably 20% by
mass or lower, and it is more preferable that α crystal is not
contained at all.

[0161] In the polylactic acid obtained by the production method of the
present invention, an organic polymer (an additional polymer compound)
which has a different structure from that of polylactic acid forms a
block copolymer with polylactic acid, and this block copolymer is
contained in the polylactic acid of the present invention. Namely, when
the polylactic acid includes, as a block copolymer, an organic polymer
having a different structure from that of polylactic acid, it is detected
that the polylactic acid is obtained by the production method of the
present invention.

[0162] The content ratio of the organic polymer having a different
structure from that of polylactic acid is from 1% by mass to 99% by mass,
and it is preferable that the content ratio is from 10% by mass to 90% by
mass.

[0163] Here, it may be confirmed that polylactic acid and an organic
polymer having a different structure from that of polylactic acid form a
block copolymer, by the following method. Further, from the ratio of
signal intensities, the component ratio of polylactic acid and the
organic polymer having a different structure from that of polylactic acid
can be determined.

1. Method of Dissolving in a Solvent that Dissolves Polylactic Acid and
the Additional Polymer Compound, and Performing NMR Measurement

[0164] After dissolving in a solvent that dissolves both the additional
polymer compound and polylactic acid, which form the block copolymer, NMR
measurement of this solution is performed. When this solution contains
the raw materials that form the block copolymer including polylactic acid
and the additional polymer compound, a signal arising from the "junction
point" of the polylactic acid and the polymer compound other than
polylactic acid is observed besides the signals arising from the
polylactic acid homopolymer and the polymer compound other than
polylactic acid. Herewith, it is confirmed that the targeted sample
contains a block copolymer including polylactic acid and an additional
polymer compound. Further, by comparing the intensities of the NMR
signals, the composition ratio of the polylactic acid and the additional
polymer compound can be determined. Note that, since, in the diblock
copolymer, there is only one junction point per one molecular chain of
the block copolymer and the number of the junction points is few, the
signal corresponding to the junction point is very weak, but by
integrating the data in accordance with a method of extending the NMR
measurement time or the like, the measurement can be conducted.

2. Method of Dissolving in a Solvent that Dissolves Polylactic Acid and
the Additional Polymer Compound, then Pouring the Resulting Solution into
a Solvent that does not Dissolve Polylactic Acid but Dissolves the
Additional Polymer Compound, to Separate the Polylactic Acid, and
Performing NMR Measurement Thereof

[0165] After dissolving in a solvent that dissolves both the additional
polymer compound and polylactic acid, the resulting solution is poured
into a solvent that does not dissolve polylactic acid but dissolves the
additional polymer compound, and the resulting precipitates are gathered,
and the precipitates are again dissolved in a solvent that dissolves both
the above components, to perform NMR measurement. When polylactic acid
forms a block copolymer together with an additional polymer compound,
signals arising from polylactic acid and the additional polymer compound
are observed, whereby the existence of the additional polymer compound is
confirmed.

[0166] When a signal arising from an additional polymer compound is
observed together with the signal arising from polylactic acid, it is
confirmed that polylactic acid and an additional polymer compound are
included. More specifically, for example, in a case in which a block
copolymer containing polylactic acid and polystyrene is included, after
dissolving in chloroform, the resulting solution is poured into
cyclohexane (which does not dissolve polylactic acid), and the
precipitates are gathered. Then, the cyclohexane may be removed from the
precipitates, and then these precipitates may be dissolved in chloroform,
followed by performing NMR measurement. Further, by comparing the
intensities of the NMR signals, the composition ratio of the polylactic
acid and the additional polymer compound can be determined.

3. Method of Performing Soxhlet Extraction Using a Solvent that does not
Dissolve Polylactic Acid but Dissolves the Additional Polymer Compound,
to Remove the Additional Polymer Compound, and Performing NMR Measurement
of the Residue

[0167] Using a solvent that does not dissolve polylactic acid but
dissolves the additional polymer compound, the molded body is
sufficiently subjected to Soxhlet extraction, and the residue is
dissolved in a solvent that dissolves both the above components, followed
by performing NMR measurement of this solution. When polylactic acid
forms a block copolymer together with an additional polymer compound,
signals arising from polylactic acid and the additional polymer compound
are observed, whereby the existence of the additional polymer compound is
confirmed.

[0168] For example, in a case in which a copolymer containing polylactic
acid and polystyrene is used, first, Soxhlet extraction may be carried
out using cyclohexane (which does not dissolve polylactic acid), then the
residue may be dissolved in chloroform, and then NMR measurement of this
solution may be conducted. Further, by comparing the intensities of the
NMR signals, the composition ratio of the polylactic acid and the
additional polymer compound can be determined.

[0169] In the present invention, the existence and content of the
additional polymer compound are confirmed using the Method 1 described
above.

[0170] The polylactic acid obtained by the method for producing stereo
complex crystals of polylactic acid of the present invention has a
melting point measured by DSC of 220° C. or higher, preferably
from 240° C. to 260° C., and thus, the polylactic acid
according to the present invention has excellent heat resistance as
compared with polylactic acids obtained by a known production method.

[0171] The polylactic acid of the present invention, which is obtained by
the production method of the present invention, has a melting point of
220° C. or higher, and therefore, like the generally used
polyethylene terephthalate (PET) which has a melting point of around
250° C., the polylactic acid of the present invention is useful in
various resin molded bodies, synthetic fibers, and the like. Further,
using the characteristics, this polylactic acid is also suitably used,
for example, for the formation of porous bodies, ion conductors, and the
like.

[0172] <Molded Body>

[0173] Hereinbelow, the molded body which is configured to include the
polylactic acid of the present invention is explained.

[0174] The molded body of the present invention contains the polylactic
acid of the present invention and an additional polymer compound that
forms a block copolymer with polylactic acid. Only the polylactic acid of
the present invention and the additional polymer compound that forms a
block copolymer with polylactic acid may be used as the molding resins,
or these components may be used by blending with a polymer compound
containing polylactic acid, an additive such as an inorganic filler or a
crystal nucleating agent (for example, a substance that accelerates
stereo complex crystallization of polylactid acid, or the like), a
solvent, an ion, a metal compound, or the like.

[0175] Examples of the polymer compound, which can be used in combination
and is other than polylactic acid, include other thermoplastic resins,
thermosetting resins, and soft thermoplastic resins; and one or more of
these polymer compounds can be added. Concerning the timing of addition,
these components may be added during the step of preparing the polymer
mixture solution or the step of removing the solvent from the polymer
mixture solution, as long as the formation of stereo complex crystals of
polylactic acid in the present invention is not damaged.

[0176] However, when the amount of the organic polymer compound to be used
in combination is large, the total weight fraction of the stereo complex
crystals becomes low, and therefore, it is preferable that the molded
body contains polylactic acid as the main component. Namely, it is
preferable that polylactic acid accounts for 10% by mass or higher of the
molding resins, and polylactic acid may account for 99% by mass of the
molding resins.

[0177] Further, examples of the inorganic additives, such as the inorganic
filler, which may be used in the present invention, include a metal
compound, an ion, a light-resisting agent, an antioxidant, and a crystal
nucleating agent for polylactic acid (for example, a substance that
accelerates stereo complex crystallization, or the like), and the
inorganic additive may also be added during the step of preparing the
polymer mixture solution or the step of removing the solvent from the
polymer mixture solution.

[0178] In a case in which a member having a desired form, such as the form
of a membrane or powder, is obtained after the solvent removing step, the
member may be designated as a membranous or powdery molded body
containing polylactic acid, without further adding a molding step. As
described above, such a molded body is also included in the molded body
of the present invention. Further, in a case in which a member having a
desired form, such as the form of a membrane or powder, is obtained after
the heat treatment step, the member may be designated as a membranous or
powdery molded body containing polylactic acid, without further adding a
molding step.

[0179] The molded body of the present invention contains the polylactic
acid of the present invention, and further contains, as described above,
an additional polymer compound that forms a block copolymer with
polylactic acid. Incorporation of the additional polymer compound makes
it possible to obtain a molded body also having a function that is
originally possessed by the additional polymer compound, such as thermal
resistance, ionic conductivity, or the like.

[0180] The molded body of the present invention is configured to include
the polylactic acid of the present invention, but the molded body of the
present invention may include components such as a polymer compound
(including polylactic acid) which is the same as or different from the
polymer compound other than polylactic acid, which forms a block
copolymer with polylactic acid, an inorganic substance, a solvent, or the
like, as a constituent material or an additive, as long as the molded
body of the present invention includes the polylactic acid of the present
invention in at least a portion of the constituent material thereof.

[0181] Accordingly, not only the polylactic acid of the present invention,
but also a molded body obtained by molding the polymer mixture used for
the production of the polylactic acid, a molded body which is obtained by
heat treating the molded body obtained by molding a substance including
the polymer mixture, and a molded body including a synthetic fiber, a
porous body, or an ion conductor, each of which is obtained from the
polylactic acid of the present invention and is described in detail
below, are included in the molded body of the present invention.

[0182] In the production of the molded body, the polylactic acid of the
present invention may be used like a resin material generally used in the
production of a molded body. In the case of imparting some functions to
the molded body of the present invention, as needs arise, known resin
materials may be used by blending, or known additives or solvents may
also be used.

[0183] For example, for producing the molded body, a filler may be added
as a reinforcing agent to the polylactic acid of the present invention,
or to a molded body containing the polylactic acid. Either an inorganic
filler or an organic filler may be used as the filler.

[0186] As to these fillers, fibrous, plate-like, or needle-like fillers
can be used. Among these fillers, fibrous inorganic fillers are
preferable, and glass fiber is particularly preferable. Further, the
aspect ratio of the filler is preferably 5 or higher, and more preferably
10 or higher. The aspect ratio of the filler is particularly preferably
100 or higher. The term "aspect ratio" indicates a value obtained by
dividing the length of a fiber by the diameter of the fiber in the case
of a fibrous filler, and a value obtained by dividing the length in the
long-period direction by the thickness in the case of a plate-like
filler.

[0187] The elastic modulus of the filler is preferably 50 GPa or higher.

[0188] In the case of using a fibrous filler as the filler, the fibrous
filler preferably has a single-fiber strength of 200 MPa or higher and
more preferably 300 MPa or higher. When the single-fiber strength is
within this range, the fibrous filler has sufficient mechanical
properties as a composite, and further, a molded body having surfaces
with excellent outside appearance is obtained even if a required amount
is added, since a sufficient reinforcing effect can be obtained even
though the amount of the filler to be mixed is reduced.

[0189] The fiber diameter of the fibrous filler is in a range of from 0.1
μm to 1 μm, and preferably in a range of from 1 μm to 500 μm.
The aspect ratio (length/diameter), which is the ratio of a length of the
fiber to the diameter, is preferably 50 or higher. When the aspect ratio
is within this range, the resin and the fiber can be mixed together well,
and a molded product having good physical properties can be obtained by
compounding. The aspect ratio is more preferably from 100 to 500, and
even more preferably from 100 to 300.

[0190] Further, the polylactic acid that forms the molded body may
contain, other than the above filler, one kind or two or more kinds of
known additives, for example, a plasticizer, an antioxidant, a light
stabilizer, an ultraviolet ray absorbent, a thermostabilizer, a
lubricant, a release agent, an antistatic agent, a flame retardant, a
foaming agent, a packing material, an antibacterial/antifungal agent, a
nucleating agent (a substance that accelerates stereo complex
crystallization of polylactic acid, or the like), a colorant including a
dye and a pigment, or the like, in addition to the above filler,
depending on the purposes.

[0191] Moreover, in the case of using the molded body as an ion conductor,
the molded body may contain, together with the polylactic acid, a
substance having ionic conductivity, for example, a metal such as lithium
or an ion thereof, an ion of, for example, an oxide, a chloride, a
fluoride, a complex, or the like, or a metal compound.

[0192] Further, in the steps for obtaining a molded body, a synthetic
fiber, or a porous body, which are described below, in the case of
allowing the polymer mixture to be in the sate of being swelled by a
solvent, the solvent may be contained, or the solvent may be newly added.
In the case of newly adding a solvent, the solvent may be the same as or
different from the solvent used in the preparation of the polymer mixture
solution. Further, the above two solvents or two or more kinds of
different solvents may be contained. In the case of containing a solvent
which is the same as the solvent used in the preparation of the polymer
mixture solution, it is not necessary to thoroughly remove the solvent in
the solvent removing step, and the polymer mixture in the state of
involving the solvent may be used for fabricating a molded body or a
synthetic fiber by, for example, kneading, extrusion, injection molding,
press molding, melt spinning, wet spinning, electrostatic spinning, or
the like. The solvent used in this process is preferably a solvent which
causes to swell polylactic acid and the additional polymer compound that
forms a block copolymer with polylactic acid, or the above-described
polymer compound (including polylactic acid) which is additionally added,
and the like. Note that, with regard to the polylactic acid, the solvent
used in the above mixture solution preparing step can be suitably used.

[0193] The thus formed resin composition obtained by adding an additional
component to the polylactic acid of the present invention, or the polymer
mixture or molded body containing the polylactic acid exhibits sufficient
strength and heat resistance, and can be suitably used for the formation
of a molded body.

[0194] Further, in the production of a molded body, the polymer mixture,
which is prepared by removing the solvent from the mixture solution
obtained in the step of producing the polylactic acid and contains the
polylactic acid, may be directly used for the production of a molded
body. This is because, since the polymer mixture contains the polylactic
acid of the present invention at a high concentration, the obtained
molded body is made to contain the polylactic acid of the present
invention by means of directly producing a molded body, other than by
means of producing the polylactic acid by using the polymer mixture as a
raw material and processing it into a molded body.

[0195] Depending on the application purpose, a molded body having a form
selected as appropriate is produced, but as to the forming method of the
molded body, any techniques for producing a molded body using a resin
composition which is generally used may be applied.

[0196] In a case in which, in the solvent removing step, the solvent
contained in the component other than polylactic acid is removed and the
removed portion becomes a fine hole, the molded body is suitably used as
a porous body. The thus obtained porous body containing the polylactic
acid of the present invention may further be subjected to heat treatment.

[0197] On the other hand, since it is thought that, in the polymer mixture
or in the molded body, polylactic acid and an additional organic polymer
compound form a phase separated structure in nano-meter order, in a case
in which fine holes are not formed in the solvent removing step and a
molded body that does not have any voids is obtained, the polylactic acid
of the present invention is suitably used as a transparent film or the
like.

[0198] As described above, the obtained molded body may further be
subjected to heat treatment, regardless the form of the molded body. The
heat treatment may be conducted in a DSC oven by placing the molded body
to be heat treated in a sample pan for DSC measurement, or the heat
treatment may be conducted using an oven, a press molding apparatus, an
air thermostat, an oil bath, or the like, as long as the apparatus can be
set to a constant temperature. The heat treatment temperature can be set
at a temperature within a range of from 60° C. to 300° C.,
the range being equal to or higher than the glass transition temperature
(Tg) but the melting point (Tm) or lower, and more preferably from
80° C. to 250° C. The heat treatment time is preferably
from 1 minute to 72 hours, and more preferably from 1 hour to 24 hours.

[0199] By performing such a heat treatment, the content of the stereo
complex crystals obtained is further increased.

[0200] As described above, by using the composition including the
polylactic acid of the present invention, from the aspects according to
the molding method, molded bodies such as a press molded product, an
injection molded product, an extrusion molded product, a vacuum-pressure
molded product, and a blow molded product; from the aspects of its form,
a film, a sheet, a plate-like body, a structure, a non-woven fabric, a
fiber, cloth, and a complex with other material; and from the aspects of
its use, an agricultural material, a fishing material, a civil
engineering/construction material, stationary, a medical supply, various
kinds of containers, and other molded bodies can be obtained,
respectively. Molding can be carried out by a commonly used method, and
there is no particular limitation on the molding method.

[0201] For example, after the solution obtained by the above-described
mixture solution preparing step is cast, the solvent is vaporized to
remove the solvent through performing the above-described solvent
removing step, thereby preparing a film-shaped product, which is then
heat treated at a temperature in a range of from 60° C. to
300° C., to produce a film having excellent heat resistance.

[0203] Examples of the use of the molded body include structural
materials, construction materials, fitting materials, temporary
construction materials, various auto parts, interior finishing materials,
sheets, and mats, which should have strength and heat resistance. The
molded body of the present invention is suitably used in a wide range of
use, and has a wide range of application.

[0204] Furthermore, in these molding steps, in the case of allowing the
polymer mixture to be in the sate of being swelled by a solvent, the
solvent may be contained, or the solvent may be newly added. In the case
of newly adding a solvent, the solvent may be the same as or different
from the solvent used in the preparation of the polymer mixture solution.
Further, the above two solvents or two or more kinds of different
solvents may be contained.

[0205] By subjecting the polymer mixture, which contains a solvent and is
in the state of being swelled, to kneading, extrusion, injection molding,
press molding, stretching (uniaxial or biaxial), or the like, there is a
case in which the plastic deformation property or stretching property of
the polymer mixture is enhanced, and a molded body having high
performance is obtained more easily. In this case, it is not necessary to
thoroughly remove the solvent in the solvent removing step, and the
polymer mixture in the state of involving the solvent may be subjected to
various kinds of molding as described above. The solvent used in this
process is preferably a solvent which causes to swell polylactic acid and
the additional polymer compound that forms a block copolymer with
polylactic acid, or the above-described polymer compound (including
polylactic acid) which is additionally added, and the like. Note that,
with regard to the polylactic acid, the solvent used in the mixture
solution preparing step can be suitably used.

[0206] After molding, these obtained molded bodies may further be
subjected repeatingly to the mixture solution preparing step, the solvent
removing step, the heat treatment step, the molding step, the perforating
step, the ion source applying step, or the like. In this case, the
frequency and order may be arbitrarily selected. For example, by
dissolving or swelling the obtained molded body again in a solvent and
performing a mixture solution preparing step, followed by performing a
solvent removing step, there is a case in which stereo complex crystals
are formed at a higher ratio. In this case, even though the conditions
for dissolving the molded body in a solvent are the same as the
conditions of the first mixture solution preparing step, there is a case
in which the once-formed stereo complex crystal does not dissolve
thoroughly and remains, and this acts as a nucleus in the solvent
removing step, the heat treatment step, the molding step, or the spinning
step, resulting in the formation of stereo complex crystals at a higher
ratio.

[0207] In the following, particularly preferable embodiments in the molded
body including the polylactic acid of the present invention are
described.

[0208] <Synthetic Fiber>

[0209] Since the polylactic acid of the present invention has excellent
heat resistance, it can be suitably used for synthetic fibers. The
synthetic fiber of the present invention is configured to include the
polylactic acid of the present invention.

[0210] The polylactic acid of the present invention has excellent
processing property, and therefore, like generally used synthetic fiber
materials, the polylactic acid of the invention can be easily molded into
a single fiber form by melt spinning, wet spinning, or the like, and can
be processed as it is to the form of fiber by using a widely used
apparatus. Further, by selecting a spinning metal mold, a modified
cross-section fiber or the like can also be formed easily.

[0211] Further, these fibers may be subjected to stretching processing for
applying molecular orientation, such as uniaxial stretching, roll rolling
(stretching), extrusion stretching, or the like.

[0212] The diameter of the synthetic fiber of the present invention is
arbitrarily selected from the range of from 0.1 μm to 1 mm, and is
preferably in a range of from 1 μm to 500 μm.

[0213] Further, as another preferable production method to obtain the
synthetic fiber of the present invention, an electrostatic spinning
method is described. The method is a method of directly applying a high
voltage to a polymer solution or a polymer melt, to form nano fibers by
electrical spinning, and specifically, a method described in
Biomacromolecules, 2006, Vol. 7, pages 3316-3320 can be applied.

[0214] In this method, after forming a cast film using the polylactic acid
of the present invention, this cast film is dissolved in chloroform (4.0
g/mol), then the resulting solution is placed in a syringe and discharged
at 0.1 mL/min. In this process, the applied voltage is -25 kV, and the
surface of the drum-shaped collection portion (having a diameter of 10
cm) is made to always revolve at 20 cm/min. As a result, fine fibers
having a diameter of from 400 nm to 970 nm and an aggregate thereof are
obtained.

[0215] The fine fibers thus obtained are used for various applications,
for example, not only for non-woven fabric, but also for a base material
for cell proliferation, a filter, or the like.

[0216] Since the synthetic fiber of the present invention has a melting
point of 240° C. or higher, in a case in which clothing such as a
shirt is produced by using this fiber, processing such as ironing or heat
press can be conducted.

[0217] Therefore, the synthetic fiber of the present invention has
excellent strength and excellent heat resistance when using, and also is
useful as a fiber or fiber product derived from plants.

[0218] Further, a renewed molded body may be produced using the synthetic
fiber including the polylactic acid. Examples thereof include a molded
body obtained by using woven fabric or non-woven fabric made from the
synthetic fiber of the present invention, and the like.

[0219] Furthermore, in the step for spinning these fibers, in the case of
allowing the polymer mixture to be in the sate of being swelled or
dissolved by a solvent, the solvent may be contained, or the solvent may
be newly added. In the case of newly adding a solvent, the solvent may be
the same as or different from the solvent used in the preparation of the
polymer mixture solution. Further, the above two solvents or two or more
kinds of different solvents may be contained. By subjecting the polymer
mixture, which contains a solvent and is in the state of being swelled or
dissolved, to wet spinning, melt spinning, electrostatic spinning, or the
like, there is a case in which a fiber of the polymer mixture is obtained
more easily. In this case, it is not necessary to thoroughly remove the
solvent in the solvent removing step, and the polymer mixture in the
state of involving the solvent may be subjected to various kinds of
molding as described above. The solvent used in this process is
preferably a solvent which causes to swell or dissolves polylactic acid
and the additional polymer compound that forms a block copolymer with
polylactic acid, or the above-described polymer compound (including
polylactic acid) which is additionally added, and the like. Note that,
with regard to the polylactic acid, the solvent used in the mixture
solution preparing step can be suitably used.

[0220] After production, these obtained fibers may further be subjected
repeatingly to the mixture solution preparing step, the solvent removing
step, the heat treatment step, the molding step, the perforating step,
the ion source applying step, or the like. In this case, the frequency
and order may be arbitrarily selected. For example, by dissolving or
swelling the obtained molded body again in a solvent and performing a
mixture solution preparing step, followed by performing a solvent
removing step, there is a case in which stereo complex crystals are
formed at a higher ratio. In this case, even though the conditions for
dissolving the molded body in a solvent are the same as the conditions of
the first mixture solution preparing step, there is a case in which the
once-formed stereo complex crystal does not dissolve thoroughly and
remains, and this acts as a nucleus in the solvent removing step, the
heat treatment step, the molding step, or the spinning step, resulting in
the formation of stereo complex crystals at a higher ratio.

[0221] <Porous Body>

[0222] Since polylactic acid and the additional organic polymer compound
form a phase separated structure in nano-meter order in the polymer
mixture or in the molded body, the polylactic acid of the present
invention can be suitably used also in the production of a porous body.
The porous body of the present invention is a porous body obtained by
decomposing and removing the additional polymer compound that forms a
block copolymer with polylactic acid, or other components (other polymer
component or additives such as an inorganic filler) from the polymer
mixture, the molded body, or the synthetic fiber, each including the
polylactic acid of the present invention.

[0223] The porous body of the present invention is obtained by preparing
or producing a polymer mixture or a molded body in a desired form
including the form of a membrane, a film, a sheet, and a fiber, each of
which is configured to include the polylactic acid of the present
invention, and thereafter, removing at least a portion of the component
which is other than polylactic acid and is contained in the polymer
mixture or the molded body, by a means such as acid etching treatment,
ultrasonic wave treatment in a solvent, or the like.

[0224] Further, in the step for producing a porous body, in the case of
allowing the polymer mixture to be in the sate of being swelled by a
solvent, the solvent may be contained, or the solvent may be newly added.
In the case of newly adding a solvent, the solvent may be the same as or
different from the solvent used in the preparation of the polymer mixture
solution. Further, the above two solvents or two or more kinds of
different solvents may be contained. A porous body may be obtained by a
method including subjecting the polymer mixture which contains a solvent
and is in the state of being swelled, to kneading, extrusion, injection
molding, press molding, stretching (uniaxial or biaxial), or the like, to
prepare a mixture of the polymer mixture and the solvent, and thereafter,
removing the solvent with reference to the above solvent removing step.
The solvent used in this process is preferably a solvent which causes to
swell polylactic acid and the additional polymer compound that forms a
block copolymer with polylactic acid, or the above-described polymer
compound (including polylactic acid) which is additionally added, and the
like. Note that, with regard to the polylactic acid, the solvent used in
the mixture solution preparing step can be suitably used.

[0225] In the formation of the porous body of the present invention, such
a perforating treatment by removing the solvent and the above-described
perforating treatment by decomposing and removing the polymer compound
other than polylactic acid may be combined, or may be performed,
repeatingly. In this case, the frequency and order of these perforating
steps may be arbitrarily selected.

[0226] After preparation, these obtained porous bodies may further be
subjected repeatingly to the mixture solution preparing step, the solvent
removing step, the heat treatment step, the molding step, the perforating
step, the ion source applying step, or the like. In this case, the
frequency and order may be arbitrarily selected. For example, by
dissolving or swelling the obtained molded body again in a solvent and
performing a mixture solution preparing step, followed by performing a
solvent removing step, there is a case in which stereo complex crystals
are formed at a higher ratio. In this case, even though the conditions
for dissolving the molded body in a solvent are the same as the
conditions of the first mixture solution preparing step, there is a case
in which the once-formed stereo complex crystal does not dissolve
thoroughly and remains, and this acts as a nucleus in the solvent
removing step, the heat treatment step, the molding step, or the spinning
step, resulting in the formation of stereo complex crystals at a higher
ratio.

[0227] The portion where the component other than polylactic acid has been
removed becomes a void, and a porous body of polylactic acid, which has a
large number of fine voids in the interior thereof, is formed. As the
means for removing the other component, the above acid etching treatment
and ultrasonic wave treatment are exemplified, but the invention is not
limited to the methods, and any method may be used as long as the
component other than polylactic acid is substantially removed by the
method. Further, these methods may be performed in combination or may be
performed repeatingly. In the case of combining plural means, the order
and frequency thereof may be arbitrarily selected. In addition, these
plural treatments may be performed at the same time.

[0228] Moreover, the porous body obtained may be further subjected to
stretching processing for applying molecular orientation, such as
uniaxial stretching, simultaneous biaxial stretching, successive biaxial
stretching, roll rolling (stretching), or extrusion stretching. The
stretching processing may be performed prior to the above-described step
of decomposing and removing the component other than polylactic acid.

[0229] The pore size of the porous body of the present invention is a
nano-order pore size, owing to the phase separated structure of the block
copolymer needed to produce stereo complex crystals of polylactic acid,
and therefore, the porous body of the present invention is a porous body
having nano-sized fine pores. This porous body also has excellent
strength and excellent heat resistance owing to the physical properties
of polylactic acid, like the molded body or the synthetic fiber of the
present invention. Further, since polylactic acid has biocompatibility,
these porous bodies can be suitably utilized as medical supplies such as
a blood purifying filter, a foothold material for cell proliferation, or
a separation membrane for implantable glucose sensor.

[0230] For example, the present inventors have found that a polymer porous
membrane can be suitably applied to a separation membrane used in
implantable glucose sensor, which is a medical equipment useful for
controlling the blood sugar level of diabetics [ACS Nano, 2009, Vol. 3,
pages 924-932], and the porous body configured to include the polylactic
acid of the present invention is also suitably utilized in the same
application. As to the porous body configured to include the polylactic
acid of the present invention, it can be said that, since the porous body
has excellent biocompatibility, it is more suitably used for implantable
applications.

[0231] Various attempts have been made to form a porous body of polylactic
acid in known literatures, and for example, in [Biomacromolecules, 2009,
Vol. 10, pages 2053-2066], a method for producing a porous body
structure, the method including melt kneading a poly-L-lactic acid (PLLA)
homopolymer and a polystyrene (PS) homopolymer, to obtain a molded film,
and then selectively extracting only the PS component using cyclohexane,
is described. However, the pore diameter size of the porous body obtained
by this method is a micro-order pore size, and under the existing
circumstances, a porous body having a nano-order fine pore diameter such
as the porous body of the invention has not been obtained yet.

[0232] Meanwhile, as the method for extracting only the PS component from
the micro-phase separated structure formed from the block copolymer,
there is a method of dipping in an excess amount of fuming nitric acid at
room temperature to undergo degradation and removal. According to this
method, the pore diameters of the fine pores can be appropriately
adjusted by adjusting the dipping time (from 1 minute to 1 hour). This
method is described in detail in the report written by the present
inventors [Macromolecules, 2006, Vol. 39, pages 3971-3974], and in
practice, the method described in the literature can be referenced.

[0233] Further, regarding the ultrasonic degradation of PS, it is known
that the molecular weight is reduced to one severalth, when processed for
about 3 hours at room temperature in the state of being dissolved in the
solvent. In the present invention, by dipping in a solvent that does not
dissolve polylactic acid but dissolves the PS component, only the PS
component can be decomposed and removed, while suppressing the
degradation of the polylactic acid component. The method of decomposing
PS using ultrasonic wave is described in detail in, for example, Polymer
Degradation and Stability, 2000, Vol. 68, pages 445-449, and in practice,
the method described in the literature can be referenced.

[0234] <Ion Conductor>

[0235] Further, since the polylactic acid of the present invention forms a
phase separated structure in nano-meter order with the additional organic
polymer compound in the polymer mixture or in the molded body, the
polylactic acid of the present invention can be suitably used also in the
production of an ion conductor. The ion conductor of the present
invention is an ion conductor obtained by applying an ion source to the
component other than polylactic acid in the polymer mixture containing
the polylactic acid of the present invention or the molded body (in this
molded body, those in the form of a membrane, a synthetic fiber, or the
like are included) which is configured to include the polylactic acid.
Further, in the porous body which is configured to include the polylactic
acid, in a case in which the component other than polylactic acid remains
as the material that forms the porous body, an ion conductor can be
obtained by applying an ion source to the remaining component other than
polylactic acid.

[0236] It should be noted that, in a case in which the polymer component,
which forms a block copolymer with polylactic acid and has a different
structure from that of polylactic acid, originally contains an ion
source, such as polystyrenesulfonic acid, a post-treatment for applying
an ion source may not be conducted, or the post-treatment may be
conducted to further increase the concentration of the ion source.

[0237] Further, in a case in which a component that becomes an ion source
has been already added in the step of preparing the polymer mixture
solution or in the step of removing the solvent contained in the polymer
mixture solution, the molded body obtained may be used as an ion
conductor without subjecting the molded body to a treatment for applying
an ion source.

[0238] The ion conductor of the present invention is obtained by, first,
preparing or producing a membranous or powdery molded body formed from
the polymer mixture which is configured to include the polylactic acid of
the present invention or a molded body which is formed by including the
polymer mixture as a portion of the raw material and has a desired form
including the form of a membrane, a film, a sheet, and a fiber, and
thereafter, applying an ion source to the component which is other than
polylactic acid and is contained in the polymer mixture or the molded
body. Here, explaining the case of using polystyrene as the component
other than polylactic acid as an example, when performing a chemical
treatment of allowing the polymer mixture containing polylactic acid and
polystyrene or the molded body to react with chlorosulfonic acid in an
appropriate solvent, the polystyrene contained in the molded body or the
like is changed to polystyrenesulfonic acid to become an ion source. In
this way, an ion source is introduced into the component other than
polylactic acid and, as a result, an ion conductor in which an ionic
conduction channel and the polylactic acid component are combined in
nano-meter size is formed.

[0239] Furthermore, after obtaining the ion conductor, the obtained ion
conductor may be further subjected to stretching processing for applying
molecular orientation, such as uniaxial stretching, simultaneous biaxial
stretching, successive biaxial stretching, roll rolling (stretching), or
extrusion stretching. With regard to the molded body which contains
polylactic acid that becomes a raw material of an ion conductor, the
stretching processing may be performed prior to the conduction of
chemical treatment or addition treatment for applying an ion source to
the component other than polylactic acid, and also in the case of
performing the stretching processing first, and then introducing an ion
source, molecular orientation can be applied to the ion conductor,
similar to the case of forming an ion conductor first and then performing
the stretching processing.

[0240] Since the ion conductor exhibits a structure having micro-sized ion
sources, a high ionic conductivity can be obtained, and also, since the
ion conductor of the present invention is configured to include a
polylactic acid having a high melting point, the ion conductor can be
suitably utilized as a fuel cell membrane that operates at a high
temperature equal to or higher than 200° C. Further, since
polylactic acid is synthesized from lactic acid which is a plant-based
raw material, it is advantageous in that a fuel cell membrane which does
not use a petroleum-based raw material can be produced in future, and the
like.

EXAMPLES

[0241] Hereinbelow, the present invention is described more specifically
with reference to Examples, but the invention is by no means limited to
the following Examples unless they are beyond the scope of the invention.

[0242] Polymerization was conducted in a 2 L five-necked flask with a
stirring bar coated with Teflon (registered trademark). Three among the
five necks were each equipped with a glass stopper through an O-ring made
of fluororesin, the fourth neck was equipped with a thermometer, and the
last one was equipped with a three-necked Y-tube. This three-necked
Y-tube was equipped with an argon/pressure reduction branch pipe, a
manometer, and a septum stopper. The pressure inside this reaction vessel
was reduced to about 1×10-3 Torr (1.33×10-1 Pa),
and the reaction vessel was heated at 275° C. for 16 hours.
Thereafter, the reaction vessel was cooled to room temperature, and then,
under a stream of argon, a burette with pure styrene (98.7 g, 0.949 mol),
a burette with pure ethylene oxide (10.0 g, 0.227 mol), and a burette
with 0.7 L of pure cyclohexane were attached to the three necks,
respectively. In this process, the burette with styrene and the burette
with cyclohexane were directly attached to the reaction vessel, but the
burette with ethylene oxide was attached through a flexible ultra-high
vacuum Swedge Lock. Note that, with regard to the ethylene oxide, the
system was immersed in an ice bath, and the pressure inside the burette
was maintained at a negative pressure.

[0243] The pressure inside the reaction apparatus was reduced, and the
operation of substituting the inside of the system with argon gas was
repeated 6 times. Further, to make sure that there was no leak in the
reaction system, the pressure inside the vessel was measured. Thereafter,
cyclohexane was added as a reaction solvent and further, a sec-butyl
lithium solution (a mixture solution of 3.28 mL of 1.29 M (molar
concentration) sec-butyl lithium and 4.93×10-3 mol of
cyclohexane) was added as an initiator from the septum stopper by using a
syringe. Note that, the sec-butyl lithium solution was placed in a dry
box until use. Styrene was gradually added to the mixture solution of
this initiator and cyclohexane. When this reaction mixture liquid was
heated to 43° C. using a water bath, the color of the reaction
mixture liquid turned orange-red. While applying pressure, the
temperature was raised to 53° C. in 10 minutes from the initiation
of the reaction, then the temperature was lowered to 42° C., and
the reaction mixed liquid was allowed to react while stirring for 4.3
hours. Thereafter, before adding ethylene oxide which is a reaction
stopping agent, the temperature was lowered to room temperature. When
ethylene oxide was added, the color of the reaction mixed liquid
immediately turned colorless. This mixture liquid was stirred at room
temperature for 14 hours, and then was taken out from the reaction vessel
under an atmosphere consisting of argon at a positive pressure. This
product was poured into a 50:50 (volume ratio) mixed liquid of 2-propanol
and methanol at room temperature, the white precipitate thus obtained was
subjected to suction filtration, followed by drying at 112° C.
under vacuum for 15 hours, to obtain PSOH. The weight average molecular
weight of the PSOH thus produced was 19,500, and the molecular weight
distribution was 1.02.

1-2. Synthesis of Polystyrene-Polylactic Acid Copolymer (PS-b-PLLA)

[0244] All the lactide polymerization reactions were carried out in a
closed dry box, and dry toluene including lactide with an initial
concentration of 1.0 M was used. Equal molar amounts of triethyl aluminum
(Et3Al) and PSOH were reacted to form an aluminum alkoxide
initiator. The diblock copolymer synthesized by using these compounds was
re-precipitated in methanol, and then filtered off by suction filtration.
The obtained block copolymer was dried at 120° C. under vacuum.
The weight average molecular weight of the poly-L-lactic acid
(PLLA)/polystyrene (PS) diblock copolymer thus obtained was 40,500, and
the molecular weight distribution was 1.1.

Synthesis Example 2

Synthesis of Poly-D-Lactic Acid (PDLA) Homopolymer

[0245] D-lactic acid monomers were dissolved in ethyl acetate anhydride,
and then purified by re-precipitation. Polymerization was conducted at
130° C. in an ampoule, which was made of glass and equipped with a
stirring bar coated with Teflon (registered trademark). Tin(I) octanoate
was added as a catalyst to petroleum ether to carry out ring-opening
polymerization. In this process, the pressure inside the ampoule tube was
reduced using a high vacuum pump, and the inside of the system was
repeatingly substituted by high purity nitrogen gas to remove volatile
impurities, the solvent, and dissolved oxygen. Thereafter, the ampoule
tube was sealed using a burner, and the temperature was raised to the
reaction temperature. After the reaction was completed, the reaction
product was taken out from the ampoule tube and was dissolved in
chloroform, and then the resulting solution was added to an excess amount
of methanol to obtain precipitates, followed by filtration and drying,
thereby obtaining a product. The weight average molecular weight of the
obtained PDLA was 19,500, and the molecular weight distribution was 1.1.

[0246] 1 g of the poly-L-lactic acid (PLLA)/polystyrene (PS) diblock
copolymer (weight average molecular weight: 40,500, molecular weight
distribution 1.1), which was formed from a PLLA polymer having a
molecular weight of 19,500 and polystyrene having a molecular weight of
21,000 and was obtained by Synthesis Example 1, and 0.5 g of the
poly-D-lactic acid (PDLA) homopolymer (weight average molecular weight:
19,500, molecular weight distribution 1.1), which was obtained by
Synthesis Example 2, were dissolved in chloroform at room temperature
(25° C.) such that the polymer concentration was 1% by mass, to
obtain a polymer mixture solution.

[0247] The polymer mixture solution thus obtained was casted on petri
dishes (diameter: 7 cm×5 dishes) made of Teflon (registered
trademark) at room temperature (25° C.), followed by drying to
remove the solvent, thereby obtaining a film-shaped polymer mixture.
Further, the resultant was dried under reduced pressure for 24 hours, to
obtain a film-shaped polymer mixture (a molded body of Example 1) (the
condition of the pressure reduction: 1 Pa).

[0248] It should be noted that the amount of the PLLA component in the
diblock copolymer (PLLA-b-PS) is about 0.5 g, which is almost equal to
the amount of the PDLA homopolymer to be added. Namely, the amount of the
polylactic acid component (PLLA+PDLA) is about 1 g, with respect to 1.5 g
of the total polymer amount in the polymer mixture solution; and
PLLA:PDLA is about 1:1. Precisely, the amount of the polylactic acid
component is [1 g×19,500/40,500+0.5 g], and PLLA:PDLA is 0.98:1.

[0249] When a cast film having a diameter of 15 cm was prepared using this
polymer mixture solution, cracks were observed at a part of the film, and
it was revealed that the uniformity was slightly inferior.

[0250] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.

[0252] The DSC chart obtained when the measurement of melting point was
carried out in Example 1 and Example 2 described below is shown in FIG.
1. In the measurement of DSC, as shown in FIG. 1, two endothermic peaks
were observed at 225° C. and 241° C., and the heat of
fusion was 42 J/g.

[0253] The DSC apparatus used for the measurement of melting point was
PYRIS 1 DSC (trade name), manufactured by PerkinElmer, Inc., and the
temperature elevation rate was 10° C./min. In this specification,
the melting peak temperature in the DSC chart recorded by the above
measurement is defined as the melting point (Tm) of the sample. It should
be noted that, in a case in which two endothermic peaks are observed as
in Example 1, the sample exhibits fluidity and cannot be suitably
utilized as a member at a temperature equal to or higher than the higher
endothermic peak temperature (melting point Tm) of the two, and
therefore, this value of melting point is an index of limit temperature
of heat resistance. In a case in which plural melting peaks appear as in
Example 1, the sample does not exhibit fluidity and is in the solid state
at the temperature equal to or lower than the highest melting peak
temperature, and therefore, the temperature of the melting peak that is
positioned at the highest temperature is defined as the melting point
(Tm) of the sample. Further, the heat of fusion (ΔHf) is calculated
from the area of the melting peak, and using this value, the SC crystal
fraction and the α crystal fraction are calculated.

[0254] Further, when measured by the means described in the Method 1
described above, it was confirmed that the film of Example 1 was a film
containing 35% by mass of polystyrene derived from the block copolymer.

[0255] The SC crystal fraction (Xsc) with respect to the amount of the
polylactic acid component (PLLA+PDLA: however, the polystyrene component
is excluded) is [{42 J/g×(1.5/0.98)}/(155 J/g)]×100=41(%).

[0256] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(42 J/g)/(155 J/g)]×100=27(%).

[0257] Here, the measurement and calculation of the content of the crystal
component are carried out with reference to the following values
described in the literature (J. Polym. Sci., Polym. Phys. Ed., Vol. 45,
p. 2632 (2007)).

[0258] The heat of fusion of a 100% α crystal of a PLLA homopolymer
or a PDLA homopolymer is 94 J/g

[0259] The heat of fusion of a 100% SC crystal of a blend of PLLA and PDLA
(PLLA:PDLA=1:1) is 155 J/g

[0260] The structure of this film-shaped molded body was observed using a
scanning probe microscope, E-SWEEP (trade name) manufactured by SII
NanoTechnology Inc., in non-contact mode. FIG. 2 is a scanning probe
microscope image showing the structure of the film-shaped porous body
formed from the polymer mixture containing the polylactic acid obtained
in Example 1. As shown in FIG. 2, it is confirmed that this film-shaped
molded body forms a porous body including a great number of holes having
a pore diameter of from 10 nm to 100 nm, the holes having been made by
removing the solvent contained in polystyrene, which is the component
other than polylactic acid, in the solvent removing process.

Example 2

[0261] Preparation of films was conducted in a manner substantially
similar to that in Example 1, except that the addition amount of the
poly-D-lactic acid (PDLA) was changed to 0.25 g, and 4 petri dishes
having a diameter of 7 cm were used. In this case, the amount of the
polylactic acid component (PLLA+PDLA) is about 0.75 g, with respect to
1.25 g of the total polymer amount in the polymer mixture solution; and
PLLA:PDLA is about 2:1. Precisely, the amount of the polylactic acid
component is [1 g×19,500/40,500+0.25 g], and PLLA:PDLA is 1.93:1.

[0262] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement was conducted, and it was revealed that the melting point
(Tm) was 244° C., and the heat of fusion was 45 J/g.

[0263] Further, the SC crystal fraction (Xsc) with respect to the amount
of the polylactic acid component (PLLA+PDLA: however, the polystyrene
component is excluded) determined by the DSC measurement is [45
J/g×(1.25/0.73)}/(155 J/g]×100=50(%).

[0264] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(45 J/g)/(155 J/g)]×100=29(%).

[0265] Further, when measured in a manner substantially similar to that in
Example 1, it was confirmed that the film of Example 2 was a film
containing 42% by mass of polystyrene derived from the block copolymer.

Example 3

[0266] A poly-D-lactic acid (PDLA)/polystyrene (PS) diblock copolymer
(weight average molecular weight: 38,000, molecular weight distribution
1.1) formed from PDLA having a molecular weight of 17,000 and polystyrene
having a molecular weight of 21,000 was synthesized using D-lactic acid
in place of L-lactic acid in Synthesis Example 1. Further, poly-L-lactic
acid having a weight average molecular weight of 17,000 and a molecular
weight distribution of 1.1 was synthesized using L-lactic acid in place
of D-lactic acid in Synthesis Example 2.1 g of this poly-D-lactic acid
(PDLA)/polystyrene (PS) diblock copolymer (PDLA-b-PS) and 0.5 g of the
poly-L-lactic acid (PLLA) were dissolved in chloroform at room
temperature (25° C.) such that the polymer concentration was 1% by
mass, to obtain a polymer mixture solution.

[0268] When a cast film having a diameter of 15 cm was prepared using the
obtained polymer mixture solution, cracks were observed at a part of the
film, and it was revealed that the uniformity was slightly inferior.

[0269] In this case, the amount of the polylactic acid component is [1
g×17,000/38,000+0.5 g], and PDLA:PLLA is 0.89:1.

[0270] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement was conducted, and it was revealed that the melting point
(Tm) was 241° C., and the heat of fusion was 42 J/g.

[0271] Accordingly, the SC crystal fraction (Xsc) with respect to the
amount of the polylactic acid component (PLLA+PDLA: however, the
polystyrene component is excluded) is [{42 J/g×(1.5/0.95)}/(155
J/g)]×100=43(%).

[0272] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(42 J/g)/(155 J/g)]×100=27(%).

[0273] Further, when measured in a manner substantially similar to that in
Example 1, it was confirmed that the film of Example 3 was a film
containing 37% by mass of polystyrene derived from the block copolymer.

[0274] The melting point and heat of fusion of each crystal obtained in
Example 1 to Example 3 are shown in the following Table 1.

[0275] A film was prepared in a manner substantially similar to that in
Example 1, and this film was placed in an aluminum pan, followed by
elevating the temperature, in an DSC oven, at a temperature elevation
rate of 10° C./min to a preset temperature in a range of from
205° C. to 230° C., then the film was maintained at the
preset temperature for 30 minutes to perform heat treatment, and
thereafter, the temperature was lowered to room temperature at a rate of
100° C./min. DSC measurement of this sample was conducted at a
temperature elevation rate of 10° C./min.

[0276] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals obtained were
all SC crystals, and the melting point (Tm) and the heat of fusion were
as described below.

[0277] Since the heat treatment temperature was changed in Example 1A, the
one that has been heat-treated at 205° C. is expressed as Example
1A-1, the one that has been heat-treated at 210° C. is expressed
as Example 1A-2, the one that has been heat-treated at 215° C. is
expressed as Example 1A-3, the one that has been heat-treated at
220° C. is expressed as Example 1A-4, the one that has been
heat-treated at 225° C. is expressed as Example 1A-5, and the one
that has been subjected to heat treatment at 230° C. is expressed
as Example 1A-6. The heat treatment time was 30 minutes in all cases.

[0278] (1A-1)

[0279] Heat treatment at 205° C.: Tm=244° C., heat of fusion
43 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 42%)

[0280] (1A-2)

[0281] Heat treatment at 210° C.: Tm=244° C., heat of fusion
46 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 45%)

[0282] (1A-3)

[0283] Heat treatment at 215° C.: Tm=243° C., heat of fusion
45 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 44%)

[0284] (1A-4)

[0285] Heat treatment at 220° C.: Tm=244° C., heat of fusion
42 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 41%)

[0286] (1A-5)

[0287] Heat treatment at 225° C.: Tm=245° C., heat of fusion
49 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 48%)

[0288] (1A-6)

[0289] Heat treatment at 230° C.: Tm=245° C., heat of fusion
44 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 43%)

[0290] The DSC chart obtained when the measurement of melting point was
carried out in Example 1A is shown in FIG. 3. Further, the melting point
and heat of fusion of each crystal obtained in Example 1A are shown in
the following Table 2.

[0291] A film was prepared in a manner substantially similar to that in
Example 1, and this film was placed in an aluminum pan, followed by
elevating the temperature, in an DSC oven, at a temperature elevation
rate of 100° C./min to the preset temperature of 230° C.,
then the film was maintained at the preset temperature for 5 minutes to 6
hours to perform heat treatment, and thereafter, the temperature was
lowered to room temperature at a rate of 100° C./min. DSC
measurement of this sample was conducted at a temperature elevation rate
of 10° C./min.

[0292] Since the heat treatment time was changed in Example 1B, the one
that has been heat-treated for 5 minutes is expressed as Example 1B-1,
the one that has been heat-treated for 30 minutes is expressed as Example
1B-2, and the one that has been heat-treated for 6 hours is expressed as
Example 1B-3. The heat treatment temperature was 230° C. in all
cases.

[0293] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals obtained were
all SC crystals, and the melting point (Tm) and the heat of fusion were
as described below.

[0294] (1B-1)

[0295] Heat treatment for 5 minutes: Tm=240° C., heat of fusion 52
J/g (the SC crystal fraction (Xsc) with respect to the amount of the PLA
component is 51%)

[0296] (1B-2)

[0297] Heat treatment for 30 minutes: Tm=245° C., heat of fusion 49
J/g (the SC crystal fraction (Xsc) with respect to the amount of the PLA
component is 48%)

[0298] (1B-3)

[0299] Heat treatment for 6 hours: Tm=245° C., heat of fusion 33
J/g (the SC crystal fraction (Xsc) with respect to the amount of the PLA
component is 32%)

[0300] The DSC chart obtained when the measurement of melting point was
carried out in Example 1B is shown in FIG. 4. Further, the melting point
and heat of fusion of each crystal obtained in Example 1B are shown in
the following Table 3.

[0302] The polymer mixture solution thus obtained was casted on petri
dishes (diameter: 7 cm×5 dishes) made of Teflon (registered
trademark) at room temperature (25° C.), followed by drying to
remove the solvent, thereby obtaining a film-shaped polymer mixture.
Further, the resultant was dried under reduced pressure for 24 hours, to
obtain a film-shaped polymer mixture (a molded body of Example 4) (the
condition of the pressure reduction: 1 Pa).

[0303] It should be noted that the amount of the PLLA component in the
diblock copolymer is 0.5 g, which is equal to the amount of the PDLA
homopolymer to be added. Namely, the amount of the polylactic acid
component (PLLA+PDLA) is 1 g, with respect to 1.54 g of the total polymer
amount in the polymer mixture solution; and PLLA:PDLA is 1:1.

[0304] When a cast film having a diameter of 15 cm was prepared using the
obtained polymer mixture solution, cracks were observed at a part of the
film, and it was revealed that the uniformity was slightly inferior.

[0305] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals contained were all SC crystals. The results of
the WAXD measurement of the film obtained in Example 4 are shown in FIG.
5. It should be noted that the vertical axis shows the diffraction
intensity (in an arbitrary unit) and the horizontal axis shows the
scattering vector (q). This figure involves the results of Comparative
Example 1-1 and Comparative Example 4, which are described below.

[0307] The DSC chart obtained when the measurement of melting point was
carried out in Example 4, as well as Example 5 and Example 6, which are
described below, is shown in FIG. 6. In the measurement of DSC, as shown
in FIG. 6, two endothermic peaks were observed at 225° C. and
244° C., and the heat of fusion was 43 J/g.

[0308] The SC crystal fraction (Xsc) with respect to the amount of the
polylactic acid component (PLLA+PDLA: however, the polystyrene component
is excluded) is [{43 J/g×(1.54/1)}/(155 J/g)]×100=43(%).

[0309] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(43 J/g)/(155 J/g)]×100=28(%).

[0310] Further, when measured in a manner substantially similar to that in
Example 1, it was confirmed that the film of Example 4 was a film
containing 35% by mass of polystyrene derived from the block copolymer.

Example 5

[0311] Preparation of a film was conducted in a manner substantially
similar to that in Example 4, except that the addition amount of the
PLLA-b-PS was changed to 1 g, and the addition amount of the
poly-D-lactic acid (PDLA) was changed to 0.32 g. In this case, the amount
of the polylactic acid component (PLLA+PDLA), with respect to 1.32 g of
the total polymer amount in the polymer mixture solution, is [1
g×19,500/40,500+0.32 g]; and PLLA:PDLA is 1.50:1.

[0312] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement was conducted, and it was revealed that the melting point
(Tm) was 245° C., and the heat of fusion was 45 J/g (FIG. 6).

[0313] Further, the SC crystal fraction (Xsc) with respect to the amount
of the polylactic acid component (PLLA+PDLA: however, the polystyrene
component is excluded) determined by the DSC measurement is [45
J/g×(1.32/0.80)}/(155 J/g]×100=48(%).

[0314] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(45 J/g)/(155 J/g)]×100=29(%).

[0315] When measured in a manner substantially similar to that in Example
1, it was confirmed that the film of Example 5 was a film containing 39%
by mass of polystyrene derived from the block copolymer.

Example 6

[0316] Preparation of a film was conducted in a manner substantially
similar to that in Example 4, except that the addition amount of the
PLLA-b-PS was changed to 1 g, and the addition amount of the
poly-D-lactic acid (PDLA) was changed to 0.16 g. In this case, the amount
of the polylactic acid component (PLLA+PDLA), with respect to 1.16 g of
the total polymer amount in the polymer mixture solution, is [1
g×19,500/40,500+0.16 g]; and PLLA:PDLA is 3.00:1.

[0317] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement was conducted, and it was revealed that the melting point
(Tm) was 244° C., and the heat of fusion was 44 J/g (FIG. 6).

[0318] Further, the SC crystal fraction (Xsc) with respect to the amount
of the polylactic acid component (PLLA+PDLA: however, the polystyrene
component is excluded) determined by the DSC measurement is [44
J/g×(1.16/0.64)}/(155 J/g]×100=51(%).

[0319] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(44 J/g)/(155 J/g)]×100=28(%).

[0320] When measured in a manner substantially similar to that in Example
1, it was confirmed that the film of Example 6 was a film containing 45%
by mass of polystyrene derived from the block copolymer.

[0321] The melting point and heat of fusion of each crystal obtained in
Example 4 to Example 6 are shown in the following Table 4.

[0322] A film was prepared in a manner substantially similar to that in
Example 4, and this film was placed in an aluminum pan, followed by
elevating the temperature, in an DSC oven, at a temperature elevation
rate of 10° C./min to a preset temperature in a range of from
205° C. to 230° C., then the film was maintained at the
preset temperature for 30 minutes to perform heat treatment, and
thereafter, the temperature was lowered to room temperature at a rate of
100° C./min. DSC measurement of this sample was conducted at a
temperature elevation rate of 10° C./min.

[0323] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals obtained were
all SC crystals, and the melting point (Tm) and the heat of fusion were
as described below.

[0324] Since the heat treatment temperature was changed from that in
Example 4, the one that has been heat-treated at 205° C. is
expressed as Example 7-1, the one that has been heat-treated at
210° C. is expressed as Example 7-2, the one that has been
heat-treated at 215° C. is expressed as Example 7-3, the one that
has been heat-treated at 220° C. is expressed as Example 7-4, the
one that has been heat-treated at 225° C. is expressed as Example
7-5, and the one that has been subjected to isothermal crystallization at
230° C. is expressed as Example 7-6. The heat treatment time was
30 minutes in all cases.

[0325] (7-1)

[0326] Heat treatment at 205° C.: Tm=244° C., heat of fusion
43 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 43%)

[0327] (7-2)

[0328] Heat treatment at 210° C.: Tm=244° C., heat of fusion
46 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 46%)

[0329] (7-3)

[0330] Heat treatment at 215° C.: Tm=243° C., heat of fusion
45 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 45%)

[0331] (7-4)

[0332] Heat treatment at 220° C.: Tm=244° C., heat of fusion
42 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 42%)

[0333] (7-5)

[0334] Heat treatment at 225° C.: Tm=245° C., heat of fusion
49 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 49%)

[0335] (7-6)

[0336] Heat treatment at 230° C.: Tm=245° C., heat of fusion
44 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 44%)

[0337] The DSC chart obtained when the measurement of melting point was
carried out in Example 7 is shown in FIG. 7. Further, the melting point
and heat of fusion of each crystal obtained in Example 7 are shown in the
following Table 5.

[0338] Preparation of a film was conducted in a manner substantially
similar to that in Example 4, except that as the poly-L-lactic acid
(PLLA)/polystyrene (PS) diblock copolymer, 1 g of a commercially
available PLLA-b-PS (trade name: P2643-SLA, manufactured by Polymer
Source, Inc.; PS molecular weight 21,000, weight average molecular weight
35,000, molecular weight distribution 1.1) in which the molecular weight
of PLLA is 14,000 was used and, as the poly-D-lactic acid (PDLA), 0.4 g
of a commercially available PDLA (trade name: P3923-LA, manufactured by
Polymer Source, Inc.; molecular weight distribution 1.2) having a
molecular weight of 16,500 was used.

[0339] In this case, the amount of the polylactic acid component is [1
g×14,000/35,000+0.4 g]; and PLLA:PDLA is 1:1.

[0340] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement was conducted, and it was revealed that the melting point
(Tm) was 245° C., and the heat of fusion was 60 J/g. The results
of the DSC measurement of the film obtained in Example 8 are shown in
FIG. 8.

[0341] Accordingly, the SC crystal fraction (Xsc) with respect to the
amount of the polylactic acid component (PLLA+PDLA: however, the
polystyrene component is excluded) is [{60 J/g×(1.4/0.8)}/(155
J/g)]×100=68(%).

[0342] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(60 J/g)/(155 J/g)]×100=39(%).

[0343] When measured in a manner substantially similar to that in Example
1, it was confirmed that the film of Example 8 was a film containing 43%
by mass of polystyrene derived from the block copolymer.

[0344] When scanning probe microscope measurement of the film of Example 8
was conducted, a smooth surface structure was observed. Therefore, with
regard to the film of Example 8, the film having a thickness of 80 μm,
the light transmittance of the film was measured using an
ultraviolet-visible light absorptiometer, model: U-3010, manufactured by
Hitachi, Ltd., and as a result, a transmission factor of 71% was obtained
at a wavelength of 560 nm. The results of the ultraviolet-visible light
absorbance measurement of the film obtained in Example 8 are shown in
FIG. 9. It can be said that, since the size of the micro-phase separated
structure formed by the block copolymer is several tens nm and is smaller
than the wavelength (several hundreds nm) of visible light, light is not
scattered, and thus, a transparent film adequate for practical use is
obtained.

[0346] The polymer mixture solution thus obtained was casted on a petri
dish (diameter: 15 cm×1 dish) made of Teflon (registered trademark)
at room temperature (25° C.), followed by drying, to obtain a
film-shaped sample having a relatively large area with a diameter of 15
cm. Further, the resulting sample was dried under reduced pressure for 24
hours. As a result, a uniform film was obtained.

[0347] In this case, the ratio of polylactic acid component (PLLA:PDLA
ratio) is 1:1.

[0348] WAXD measurement of the obtained film was conducted, and it was
revealed that the crystals incorporated in the film were all SC crystals.
DSC measurement of this film was conducted, and it was revealed that the
melting point (Tm) was 227° C., and the heat of fusion (ΔHf)
was 36 J/g. The results of the DSC measurement of the film obtained in
Example 9 are shown in FIG. 10.

[0349] The SC crystal fraction (Xsc) with respect to the amount of the
polylactic acid component (PLLA+PDLA: however, the polystyrene component
is excluded) is [{36 J/g×(1.54/1)}/(155 J/g)]×100=36(%).

[0350] The SC crystal fraction with respect to the total amount of the
polymer compounds is [(36 J/g)/(155 J/g)]×100=23(%).

[0351] By comparing Example 4 and Example 9, it is understood that, when a
PDLA homopolymer having a high molecular weight is used, the uniformity
of the film obtained is improved, and a uniform molded body film having a
larger area can be obtained.

[0352] When measured in a manner substantially similar to that in Example
1, it was confirmed that the film of Example 9 was a film containing 35%
by mass of polystyrene derived from the block copolymer.

Example 10

[0353] A film was prepared in a manner substantially similar to that in
Example 9, and this film was placed in a vacuum oven (the condition of
the pressure reduction: 1 Pa) at room temperature, and the temperature
was elevated to a preset temperature in a range of from 150° C. to
225° C., and then the film was maintained at the preset
temperature for 30 minutes to perform heat treatment, and thereafter, the
resulting film was left to cool to room temperature. DSC measurement of
this sample was conducted at a temperature elevation rate of 10°
C./min.

[0354] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals obtained were
all SC crystals, and the melting point (Tm) and the heat of fusion were
as described below.

[0355] Since the heat treatment temperature was changed in Example 10, the
one that has been heat-treated at 150° C. is expressed as Example
10-1, the one that has been heat-treated at 175° C. is expressed
as Example 10-2, the one that has been heat-treated at 200° C. is
expressed as Example 10-3, the one that has been heat-treated at
205° C. is expressed as Example 10-4, the one that has been
heat-treated at 210° C. is expressed as Example 10-5, the one that
has been heat-treated at 215° C. is expressed as Example 10-6, the
one that has been heat-treated at 220° C. is expressed as Example
10-7, and the one that has been heat-treated at 225° C. is
expressed as Example 10-8. The heat treatment time was 30 minutes in all
cases.

[0356] (10-1)

[0357] Heat treatment at 150° C.: Tm=227° C., heat of fusion
47 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 47%)

[0358] (10-2)

[0359] Heat treatment at 175° C.: Tm=226° C., heat of fusion
46 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 46%)

[0360] (10-3)

[0361] Heat treatment at 200° C.: Tm=226° C., heat of fusion
51 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 51%)

[0362] (10-4)

[0363] Heat treatment at 205° C.: Tm=225° C., heat of fusion
57 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 57%)

[0364] (10-5)

[0365] Heat treatment at 210° C.: Tm=225° C., heat of fusion
56 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 56%)

[0366] (10-6)

[0367] Heat treatment at 215° C.: Tm=227° C., heat of fusion
58 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 58%)

[0368] (10-7)

[0369] Heat treatment at 220° C.: Tm=230° C., heat of fusion
58 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 58%)

[0370] (10-8)

[0371] Heat treatment at 225° C.: Tm=235° C., heat of fusion
58 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 58%)

[0372] The DSC chart obtained when the measurement of melting point was
carried out in Example 10 is shown in FIG. 11. Further, the melting point
and heat of fusion of each crystal obtained in Example 10 are shown in
the following Table 6.

[0373] Heat treatment was conducted in a vacuum oven in a manner
substantially similar to that in Example 10, except that the heat
treatment time was changed to 24 hours, and thereafter, the resulting
sample was left to cool to room temperature. DSC measurement of this
sample was conducted at a temperature elevation rate of 10°
C./min.

[0374] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals obtained were
all SC crystals, and the melting point (Tm) and the heat of fusion were
as described below.

[0375] Since the heat treatment temperature was changed in Example 11, the
one that has been heat-treated at 150° C. is expressed as Example
11-1, the one that has been heat-treated at 175° C. is expressed
as Example 11-2, the one that has been heat-treated at 200° C. is
expressed as Example 11-3, the one that has been heat-treated at
205° C. is expressed as Example 11-4, the one that has been
heat-treated at 210° C. is expressed as Example 11-5, the one that
has been heat-treated at 215° C. is expressed as Example 11-6, and
the one that has been heat-treated at 220° C. is expressed as
Example 11-7. The heat treatment time was 24 hours in all cases.

[0376] (11-1)

[0377] Heat treatment at 150° C.: Tm=227° C., heat of fusion
48 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 48%)

[0378] (11-2)

[0379] Heat treatment at 175° C.: Tm=226° C., heat of fusion
51 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 51%)

[0380] (11-3)

[0381] Heat treatment at 200° C.: Tm=225° C., heat of fusion
62 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 62%)

[0382] (11-4)

[0383] Heat treatment at 205° C.: Tm=224° C., heat of fusion
66 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 66%)

[0384] (11-5)

[0385] Heat treatment at 210° C.: Tm=227° C., heat of fusion
72 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 72%)

[0386] (11-6)

[0387] Heat treatment at 215° C.: Tm=232° C., heat of fusion
73 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 73%)

[0388] (11-7)

[0389] Heat treatment at 220° C.: Tm=234° C., heat of fusion
81 J/g (the SC crystal fraction (Xsc) with respect to the amount of the
PLA component is 81%)

[0390] The DSC chart obtained when the measurement of melting point was
carried out in Example 11 is shown in FIG. 12. Further, the melting point
and heat of fusion of each crystal obtained in Example 11 are shown in
the following Table 7.

[0392] Since the crystallization temperature was changed in Comparative
Example 1, the one that has been isothermally crystallized at 115°
C. is expressed as Comparative Example 1-1, the one that has been
isothermally crystallized at 120° C. is expressed as Comparative
Example 1-2, the one that has been isothermally crystallized at
125° C. is expressed as Comparative Example 1-3, and the one that
has been isothermally crystallized at 130° C. is expressed as
Comparative Example 1-4.

[0393] WAXD measurement (FIG. 5) of Comparative Example 1-1 was conducted
in a manner substantially similar to that in Example 1, and it was
revealed that the crystals obtained were all α crystals, and the
melting point (Tm) and the heat of fusion were as described below.

Comparative Example 1-1

[0394] Crystallization at 115° C.: Tm=172° C., heat of
fusion 9.7 J/g (the α crystal fraction (X.sub.α) with respect
to the amount of the PLA component is 21%)

Comparative Example 1-2

[0395] Crystallization at 120° C.: Tm=169° C., heat of
fusion 7.4 J/g (the α crystal fraction (X.sub.α) with respect
to the amount of the PLA component is 16%)

Comparative Example 1-3

[0396] Crystallization at 125° C.: Tm=169° C., heat of
fusion 4.5 J/g (the α crystal fraction (X.sub.α) with respect
to the amount of the PLA component is 9.6%)

Comparative Example 1-4

[0397] Crystallization at 130° C.: Tm=169° C., heat of
fusion 4.9 J/g (the α crystal fraction (X.sub.α) with respect
to the amount of the PLA component is 10%)

[0398] The DSC chart obtained when the measurement of melting point was
carried out in Comparative Example 1 is shown in FIG. 13. Further, the
melting point and heat of fusion of each crystal obtained in Comparative
Example 1 are shown in the following Table 8.

[0399] As described in Table 1 to Table 7, the polylactic acids according
to Example 1 to Example 11, which were obtained by the production method
of the present invention, have a high melting point, and exhibit
excellent heat resistance, as compared with Comparative Example 1, which
was obtained by subjecting the diblock copolymer, that is a raw material,
to melt heat treatment, and then crystallization. Further, by the method
described in Comparative Example 1, stereo complex crystals were not
obtained, and it is understood that the polylactic acid thus obtained has
a low melting point.

Comparative Example 2

[0400] The poly-L-lactic acid (PLLA)/polystyrene (PS) diblock copolymer
(PLLA molecular weight 19,500, PS molecular weight 21,000, molecular
weight distribution 1.1) obtained in Synthesis Example 1 was dissolved in
p-xylene at 130° C., such that the polymer concentration was 1% by
weight. This was casted on a petri dish made of Teflon (registered
trademark) at room temperature, followed by drying. Further, the
resultant was dried under reduced pressure for 24 hours.

[0401] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals thus obtained
were all α crystals, and from the DSC measurement, it was revealed
that Tm=165° C.

[0402] From the results, it is understood that stereo complex crystals are
not obtained by only preparing a solution of the diblock copolymer, that
is a raw material, and then casting the solution, and that the melting
point of the obtained polylactic acid is low.

Comparative Example 3

[0403] 0.5 g of a poly-L-lactic acid (PLLA) homopolymer (trade name:
LACEA, manufactured by Mitsui Chemicals, Inc.; molecular weight 230,000)
and 0.5 g of a poly-D-lactic acid (PDLA) homopolymer (manufactured by
PURAC; molecular weight 230,000) were dissolved in chloroform at room
temperature (25° C.), such that the total polymer concentration
was 1% by mass, thereby obtaining a polymer mixture solution. This was
casted in a manner substantially similar to that in Example 1, followed
by drying. Further, the resultant was dried under reduced pressure for 24
hours.

[0404] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals thus obtained
were a mixture of α crystals and SC crystals, and

[0406] From the results, it is understood that sufficient stereo complex
crystals are not produced by the method including mixing a PLLA
homopolymer and a PDLA homopolymer, each having a high molecular weight,
to obtain a polymer mixture solution, and that the melting point of the
stereo complex crystal thus obtained is low as compared with Example 1 to
Example 11.

Comparative Example 4

[0407] Next, according to the method described in non-patent document 2
[Polymer, Vol. 49, page 5670 (2008)], 0.5 g of a poly-L-lactic acid
(PLLA) homopolymer (molecular weight 36,000) and 0.5 g of a poly-D-lactic
acid (PDLA) homopolymer (molecular weight 19,000) were dissolved in
chloroform at room temperature (25° C.), such that the total
polymer concentration was 1% by mass, thereby obtaining a polymer mixture
solution. This was casted in a manner substantially similar to that in
Example 1, followed by drying. Further, the resultant was dried under
reduced pressure for 24 hours, to obtain a film.

[0408] WAXD measurement was conducted in a manner substantially similar to
that in Example 1, and it was revealed that the crystals thus obtained
were all SC crystals (FIG. 5), and from the DSC measurement, it was
revealed that Tm=216° C., and the heat of fusion was 64 J/g (the
SC crystal fraction was 41%).

[0409] In conclusion, stereo complex crystals were obtained at a high
content ratio by using a PLLA homopolymer and a PDLA homopolymer, each
having a relatively low molecular weight, and the heat of fusion was
great, however the melting temperature was low, since the molecular
weight was low and the mobility was not restricted, and thus, a
polylactic acid having heat resistance sufficient for the formation of
synthetic fibers or molded bodies was not obtained.

[0410] From the results of the above examples and comparative examples, in
a case in which the molecular weights of the polylactic acids used are
low, SC crystals are formed to some extent also by mixing equal amounts
of PLLA homopolymer+PDLA homopolymer, but the melting point thereof is
low, and is 216° C. at best.

[0411] On the contrary, in the examples according to the production method
of the present invention, polylactic acids which contain stereo complex
crystals with high efficiency and have higher melting points than those
of the comparative examples were obtained. The polylactic acids of the
present invention obtained by the production method described in Example
1 to Example 11 have a high melting temperature and exhibit excellent
heat resistance, and therefore, it is understood that the polylactic
acids of the present invention are useful for molded bodies or fiber
products to be formed by thermal processing. Further, a porous body can
be obtained by decomposing and removing the component other than
polylactic acid from the molded body or fiber.

Example 12

Production of Molded Body

[0412] As shown in FIG. 14, polyimide membrane 2 for separating which had
a thickness of 125 μm was placed on disk-shaped stainless-steel plate
1 having a size of 110 mmφ in diameter×2 mm in thickness, then
substance 3 (a stainless-steel thin plate with a rectangular window)
prepared by hollowing out a disk-shaped stainless-steel plate having a
size of 110 mmφ in diameter×0.3 mm in thickness to have a
rectangular window having a size of 30 mm×30 mm was placed, and
then 1 g of film 4 obtained in Example 1 was placed on the interior of
the window. On the structure thus obtained, polyimide membrane 5 for
separating which had a thickness of 125 μm was placed, and further,
disk-shaped stainless-steel plate 6 having a size of 110 mmφ in
diameter×2 mm in thickness was placed thereon.

[0413] The whole laminated body was placed between the upper plate and the
lower plate of a press machine (manufactured by Baldwin Co., Ltd.)
provided in a vacuum chamber at room temperature and, after reducing the
pressure to 1.33×10-1 Pa using a rotary pump, the upper plate
and the lower plate were moved to make the distance closer as possible
such that no stress was applied, followed by heating at 250° C.,
and the temperature was maintained at 250° C. for 5 minutes, and
thereafter, while maintaining the state of applying pressure with a
pressure of 4.5 MPa (cylinder pressure 60 Pa), the power source of the
heater was turned off, and the temperature was slowly cooled to room
temperature under reduced pressure. Thereafter, the vacuum chamber was
opened and a molded film (a molded body formed from the polylactic acid
obtained in Example 1) of Example 12 was taken out.

[0414] The tensile breaking strength of the molded film thus obtained was
measured. The measurement of this mechanical property was carried out,
using a universal testing machine RTC-1325A manufactured by Baldwin Co.,
Ltd., at room temperature. From the molded film, sample pieces in a
rectangular strip shape (straight line portion 30 mm, width 5 mm) were
cut out, and tensile testing was carried out at a cross-head speed of 60
mm/min. As a result, it was revealed that the tensile breaking strength
of the obtained film was 30 MPa.

[0415] Further, the melting point of the molded body film was measured in
a manner substantially similar to that in Example 1, and it was revealed
that the melting point owing to the raw material was 241° C.

[0416] From the results of Example 12, it is understood that the molded
body formed from the polylactic acid of the present invention, which is
obtained by the production method of the present invention, has excellent
breaking strength even though it has experienced a molding temperature of
250° C., and herewith, the polylactic acid of the present
invention can be suitably used for the production of various molded
bodies such as heating and pressurizing molding.

Example 13

[0417] Instead of using the stainless-steel thin plate 3 with a
rectangular window in FIG. 14, substance 3 (a polyimide membrane with a
rectangular window) prepared by hollowing out a polyimide membrane, which
had been cut into a shape of a disk having a size of 110 mmφ in
diameter×50 μm in thickness, to have a rectangular window having
a size of 30 mm×30 mm was used. Namely, polyimide membrane 2 for
separating which had a thickness of 125 μm was placed on disk-shaped
stainless-steel plate 1 having a size of 110 mmφ in diameter×2
mm in thickness, then the polyimide membrane 3 (having a thickness of 50
μm) with a rectangular window was placed, and then a sheet of the film
obtained in Example 4 was placed on the interior of the window. On the
structure thus obtained, polyimide membrane 5 for separating which had a
thickness of 125 μm was placed, and further, disk-shaped
stainless-steel plate 6 having a size of 110 mmφ in diameter×2
mm in thickness was placed thereon.

[0418] The whole laminated body was placed between the upper plate and the
lower plate of a press machine (manufactured by Baldwin Co., Ltd.)
provided in a vacuum chamber at room temperature and, after reducing the
pressure to 1.33×10-1 Pa using a rotary pump, the upper plate
and the lower plate were moved to make the distance closer as possible
such that no stress was applied, followed by heating at 225° C.,
and the temperature was maintained at 225° C. for 30 minutes, and
thereafter, while maintaining pressing with a pressure at a cylinder
pressure of 10 MPa, the power source of the heater was turned off, and
the temperature was slowly cooled to room temperature under reduced
pressure. Thereafter, the vacuum chamber was opened and a molded film of
Example 13 was taken out.

[0419] The tensile breaking strength of the molded film thus obtained was
measured. The measurement of this mechanical property was carried out,
using a universal testing machine RTC-1325A manufactured by Baldwin Co.,
Ltd., at room temperature. From the molded film, sample pieces in a
rectangular strip shape (straight line portion 30 mm, width 5 mm) were
cut out and tensile testing was carried out at a cross-head speed of 60
mm/min. As a result, it was revealed that the tensile breaking strength
of the obtained film was 10 MPa. From this result, it is understood that
the molded body formed from the polylactic acid of the present invention,
which is obtained by the production method of the present invention, has
excellent breaking strength, even though it was pressed at a temperature
equal to or lower than the melting point.

[0420] The surface structure of the film obtained in Example 13 was
observed by a scanning probe microscope. The observation image thus
obtained is shown in FIG. 15. (B) is an enlarged view of the portion
surrounded by dotted lines shown in (A). A networked linking structure
owing to the micro-phase separated structure of the block copolymer can
be observed, and it is thought that this structure has become a skeleton
to provide a molded body having excellent strength.

Example 14

Production of Porous Body

[0421] The film obtained in Example 1 was cut into a size of 30
mm×30 mm, and placed in a 50 mL beaker, and to this, 30 mL of
cyclohexane were added, and this was treated using an ultrasonic
homogenizer (trade name: UH-600S, manufactured by SMT CO., LTD.) with an
output power of 600 W and a frequency of 20 Hz, at room temperature for 6
hours. The resultant was taken out, and then washed three times with an
excess amount of cyclohexane to remove the polystyrene component that has
been decomposed by the ultrasonic treatment, thereby obtaining a porous
body having a large number of fine holes owing to the polystyrene
portions that had been removed.

[0422] The structure of this porous membrane was observed using a scanning
probe microscope, E-SWEEP (trade name), manufactured by SII
NanoTechnology Inc., in non-contact mode. As a result, as shown in FIG.
16, it was confirmed that this porous membrane was a porous body having a
porous structure with a pore diameter of from 10 nm to 100 nm.

[0423] In the porous body of Example 14, the holes are linked to the deep
internal of the membrane, and since the porous body of Example 14 has a
high melting point owing to the polylactic acid of the present invention,
which is the raw material, the porous body has excellent heat resistance
and excellent moldability, and is suitably used for various applications
such as industrial materials such as a chemical filter or a lithium ion
battery separator, or medical supplies such as a blood purifying filter,
a foothold material for cell proliferation, or a separation membrane for
implantable glucose sensor.

[0424] <Evaluation of Porous Body>

[0425] Evaluation of the molecule permeability of the porous membrane was
performed with reference to the literature [ACS Nano, 2009, Vol. 3, pages
924-932] reported by the present inventors. A membrane permeation
apparatus (trade name: PERMCELL, manufactured by Vidrex Co., Ltd.) is
used, and the porous membrane prepared in Example 14 is held at the
aperture portion (membrane area: 5 cm2) between the glass cells
(volume: 50 mL) separated into two parts, which is held by a clip through
an O-ring. Thereafter, one of the cells is filled with an aqueous
solution of D-glucose having a concentration of 100 mM (mmol/L), and the
other is filled with pure water. The solutions in the two cells are
stirred (at room temperature) for a constant time with a stirring bar
(diameter 3 mm, length 7 mm) made of Teflon (registered trademark), and
then a portion of the solution in the cell that has been filled with
water at the beginning is taken out, to measure the index of refraction.
In this process, by measuring the indexes of refraction of plural
solutions with known glucose concentrations, an analytical curve of
"index of refraction" versus "glucose concentration" can be drawn, and
according to this analytical curve, the glucose concentration is
calculated from the index of refraction.

[0428] As a result, when the porous membrane (having a thickness of about
75 μm) obtained in Example 14 was used, the glucose concentration
measured after stirring for 3 hours was 5 mM. From this, it was confirmed
that glucose had passed through the porous membrane and had moved to the
cell at the opposite side, and thus, it was confirmed that the porous
membrane obtained in Example 14 had communicating holes.

[0429] When the same evaluation was performed using the molded body film
(having a thickness of about 60 μm) obtained in Example 12, which had
not been subjected to etching, as a contrast example, the glucose
concentration was 0.1 mM, and thus, it is understood that through holes
were not formed in the molded body film obtained in Example 12. Further,
when the same measurement was performed using a commercially available
alumina porous membrane (trade name: ANODISC MEMBRANE FILTER 25,
manufactured by Whatman; construction material: alumina, membrane
thickness: 60 μm, percentage of voids: from 25% to 50%), the glucose
concentration was 50 mM, and thus, it was realized that glucose had
permeated thoroughly. Accordingly, it was confirmed that the porous
membrane obtained in Example 14 was a porous body having fine through
holes.

Example 15

Production of Ion Conductor

[0430] The film obtained in Example 1 was placed in a glass petri dish,
immersed in a cyclohexane solution of chlorosulfonic acid, which had been
prepared to have a concentration of 0.2 mol/L, and was treated at room
temperature for one hour. The treated membrane was washed three times
with cyclohexane, and this was dried under reduced pressure at room
temperature for 24 hours to remove the remaining solvent, and then the
resulting membrane was further washed three times with ion exchanged
water, followed by drying under reduced pressure at room temperature for
a period of 6 hours or more, thereby obtaining an ionic (protonic)
conducting membrane.

[0431] The sulfonation degree, water content, and protonic conductance of
this ionic conducting membrane were measured, according to JP-A No.
2008-248116, which is the previous patent of the present inventors.

1. Sulfonation Degree

[0432] The sulfonation degree was calculated according to the following
equation.

Sulfonation degree (%)=(Number of moles of the sulfonic acid groups
substituted through sulfonation treatment/Number of moles of benzene
rings)×100

2. Water Content

[0433] The weight of the membrane in the state of being saturated with
water, which was prepared by immersing the membrane in ion exchanged
water at room temperature (25° C.) for 24 hours, and the weight of
the membrane after the membrane was dried under reduced pressure at
50° C. for 8 hours and then at 100° C. for 24 hours were
measured, and the water content was determined according to the following
equation.

Water content (%)=(MW-MD)×100/MD

[0434] MW: the weight of the membrane in the state of being saturated
with water

[0435] MD: the weight of the membrane after drying

3. Protonic Conductance

[0436] The protonic conductance was measured in accordance with the
alternating current impedance method. The measurement conditions are as
follows.

[0437] From the number average molecular weight of the block copolymer
(including the PLLA component) that had been subjected to sulfonation and
the number of styrene units in the block copolymers used as the raw
material, the ion exchange capacity was calculated as follows.

Ew=Molecular weight per one sulfonic acid group

[0438] With regard to the obtained ionic conducting membrane, the results
obtained by performing these measurements are shown below.

[0440] As a contrast example, the same measurements were performed using
NAFION NRE 211CS (trade name, manufactured by DuPont), which is a
commercially available perfluorocarbon sulfonic acid membrane. The
results are shown below.

[0441] As shown above, it is understood that, also in the comparison with
the commercially available protonic conducting membrane, that is the
contrast example, although the numeric values are slightly smaller, the
ionic conducing membrane of the present invention has achieved
practically non-problematic protonic conductance and ion exchange
capacity, and thus, the ionic conducting membrane of the present
invention is noticed as an electric conducting membrane which is
synthesized from lactic acid that is a plant-based raw material, has
biocompatibility, and does not use a petroleum-based raw material.

Example 16

[0442] The film obtained in Example 11-7 was placed in a glass petri dish,
immersed in a cyclohexane solution of chlorosulfonic acid which had been
prepared to have a concentration of 0.2 mol/L, and was treated at room
temperature for three hours. The treated membrane was washed three times
with cyclohexane, and this was dried under reduced pressure at room
temperature for 24 hours to remove the remaining solvent, and then the
resulting membrane was further washed three times with ion exchanged
water, followed by drying under reduced pressure at room temperature for
a period of 6 hours or more, thereby obtaining an ionic (protonic)
conducting membrane.

[0443] Measurements of sulfonation degree, water content, and protonic
conductance of this ionic conducting membrane were performed in a manner
substantially similar to that in Example 15. As a result, the following
values were obtained.